hybrid locomotive

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See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/351512331 Traction Simulator for locomotive bogie wheels Experiment Findings · May 2021 CITATIONS 0 READS 24 1 author: Some of the authors of this publication are also working on these related projects: Hybrid Locomotive Powered from Hydrogen Fuel Cells with predictive wheel diameter compensation of each wheel providing Slip/Slide control using ac traction View project Ph D related to Hydrogen Powered locomotives View project Bernard Schaffler Queensland University of Technology 9 PUBLICATIONS 0 CITATIONS SEE PROFILE All content following this page was uploaded by Bernard Schaffler on 19 May 2021. The user has requested enhancement of the downloaded file.

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Page 1: Hybrid Locomotive

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/351512331

Traction Simulator for locomotive bogie wheels

Experiment Findings · May 2021

CITATIONS

0READS

24

1 author:

Some of the authors of this publication are also working on these related projects:

Hybrid Locomotive Powered from Hydrogen Fuel Cells with predictive wheel diameter compensation of each wheel providing Slip/Slide control using ac traction View

project

Ph D related to Hydrogen Powered locomotives View project

Bernard Schaffler

Queensland University of Technology

9 PUBLICATIONS   0 CITATIONS   

SEE PROFILE

All content following this page was uploaded by Bernard Schaffler on 19 May 2021.

The user has requested enhancement of the downloaded file.

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Hybrid Locomotive

Hybrid Locomotive Powered from Hydrogen Fuel Cells including Slip/Slide control and predictive wheel diameter

compensation of each wheel powered by DTC inverters using permanent magnet AC traction motors

A development to assist Climate Change

Proposed PhD thesis By Bernard Schaffler. BSc Eng. MSc Eng. FIEAust. CPEng. MIEEE

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Index Page Heading Title

3 Synopsis 1 Power from Hydrogen Fuel Cell

6 1.1 Hydrogen Fuel Cell

8 1.2 Hybrid Operation

10 Hybrid Circuit Diagram (Figure 4)

13 Synopsis 2 Slip/Slide Control

13 2.1 Prior Art for Slip/Slide Control

16 2.2 Back Ground of Traction Control

17 2.3 Functionality of Locomotive Wheel Slip/Slide Control

18 2.4 Summary of Slip/Slide Invention

19 2.5 Brief description of drawing used

21 2.6 The Invention

22 2.7 Predictive Topology

24 2.8 Calibration

25 2.9 The Traction Simulation unit (figure 8)

25 3.1 Direct Torque Control (DCT)

26 3.2 DCT Control Topology

29 3.3 The Active Front End Inverter

30 3.4 Basic Active Front End Inverter Scheme

30 3.5 Principle of operation of the Active Front End Inverter

32 3.6 Control Strategy

32 3.7 Step Changes to the Active Front End Inverter

34 3.8 Conclusion of Active Front End Inverter

34 4 Locomotive Master Control System (figure 4)

36 4.1 Battery Charging on a locomotive

37 5 Wheels on Rolling Stock (figure 18)

38 6 Principle of Adhesion Control

38 6.1 Tractive Effort

39 6.2 The Image of Motion Equation

44 7 Reduced Carbon Emission using AC Traction

45 8 General Information about Existing Motors

45 8.1 Existing Diesel Locomotive Systems

46 8.2 Major Sub-System – Auxiliary System

47 8.3 Major Sub-System – Traction

47 9 Locomotive Vigilance Control

47 10 Principle and Comparison

49 Transparent Picture of DO-DO hydrogen locomotive

49 Transparent Picture of CO-CO diesel locomotive

50 11 Typical Specification and Technical Information

51 12 Locomotive Wheel Data Table

51 13 Traction and Braking Effort Diagram

52 14 Locomotive whole life conclusion

55 15 References

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Hybrid Locomotive Powered from Hydrogen Fuel Cells including Slip/Slide control and predictive wheel diameter

compensation of each wheel powered by DTC inverters using permanent magnet AC traction motors

SYNOPSIS 1: Power from Hydrogen Fuel Cell Hybrid Hydrogen fuel cell are proposed for Shunter Locomotives to eliminate carbon emission. (This can be extended later for 6 and 8 axle locomotives) The development will focus on:

1. Complete removal of diesel engine from existing shunter locomotives.

2. Removed carbon emissions by using Hydrogen fuel cells where the exhaust is pure

water.

3. Significant reduction in fuel running costs.

4. Significant speed of refuelling the locomotive.

Initial steps towards using hydrogen for transport The world is focused on reducing carbon emissions. Little attention has been paid to the carbon emission from diesel locomotives – both freight and passenger. There are thousands of diesel locomotives worldwide and Australia is one of the key offenders. See figure 1 below.

Figure 1 Electrified Chart

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There is an urgent need to provide hydrogen fuelled locomotives in Australia because of the long distance travelled by train. To apply electric rail tracks is a very costly exercise. In Australia the majority of lines are not electrified because of the long distances. Australia has 36,064 km of tracks. The percentage of electrified tracks is less than 15% but growing. Figure 1 shows electrification of tracks in various counties are shown. The figure shows that whatever is electrified and the rest has to be powered mainly by diesel power. Switzerland has to be the obvious leader because so many of their tracks travel through mountain tunnels. Some apprehension around hydrogen as a fuel source is perhaps understandable considering the unfortunate history of hydrogen-filled dirigibles, namely airships such as the ill-fated British R101 and the German Hindenburg. But hydrogen-powered trains have been emerging as a viable – and much safer – means of transport.

The UK has 42% of its route miles electrified, according to the Institution of Mechanical Engineers, meaning those trains are ready to become zero-carbon, if they use a renewable source of power. A single line running to London from Hampshire is currently the only one in the world to run solely on solar power. However, the remaining 58% of UK track is not yet electrified, so diesel trains are still needed to keep those areas connected by rail. One of the most exciting prospects for hydrogen is the transport sector – one of Australia’s largest end user of energy. Analysis by the International Energy Agency already shows hydrogen to be cost-competitive in selected uses. Many believe that hydrogen has a role to play in industrial processes, and for powering heavy-duty vehicles, including ocean-going ships, locomotives, aircraft and cars. (see H2X for details of Australian cars to be built in Port Kembla.) There are several ways to produce hydrogen, but almost all of it currently in production uses methane (natural gas) as the feedstock, with non-renewable energy powering that production. Hydrogen produced by this process is called grey hydrogen, or blue hydrogen if carbon-capture technology is used to capture the emissions released during production. Hydrogen can also be produced from water via an electrolysis process, using renewable energy—this is known as green hydrogen. Currently, this makes up less than one percent of the hydrogen being produced. (Most hydrogen consumed today is used for industrial processes, including oil refining.) Theoretically, green hydrogen could neatly solve two problems in a decarbonized economy:

1st, renewable energy sources sometimes supply more energy than needed to meet current demand, and if this energy can’t be conveniently stored, it is wasted; 2nd, in some applications (aviation, ocean shipping, industrial processes) battery-electric solutions have drawbacks, and hydrogen will be a viable alternative.

Rosy hydrogen is excess energy from large renewable energy sources such as offshore wind farms and would be used to generate green hydrogen through electrolysis, which would then be used to power aircraft, ships and locomotives. This is the scenario that is being presented by oil companies and their representatives. The main problem is that, by all accounts it is probably decades away from being viable at scale. Hydrogen fuel carries much more energy than the equivalent weight of batteries. It complements battery electric vehicle technology, by providing a viable alternative for powering freight trains carrying heavy loads and travelling long distances. Shorter refuelling times can support business productivity and consumer convenience.

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A study from the consultancy Wood Mackenzie predicts that grey hydrogen will remain the cheapest type through to 2040. Other studies say green hydrogen could be cost-competitive against diesel by 2030—but if the current pace of electrification continues, diesel may well be obsolete by then, and in any case, green hydrogen won’t be competing against diesel fuel, but rather against battery storage, which is already in use at utility scale today, and is steadily growing cheaper. Governments have a shared vision of hydrogen being a clean, cost-competitive fuel option for Australian land and transport, in particular for heavy-duty and long-range transport applications.

Governments support an adaptive approach to building demand for hydrogen as a transport

fuel. The initial focus will be on transport tasks that do not require an extensive network of

refuelling stations and offer compelling performance and industry development advantages. Governments in UK, Europe, USA and Canada also support refuelling stations on major freight and passenger road corridors to support greater range for hydrogen vehicles. Preliminary work to map some of these requirements has already begun. Hydrogen is the simplest and most abundant element in the universe, but it rarely exists as a gas on Earth—it must be separated from other elements. Hydrogen can be produced from diverse, domestic resources, including fossil fuels, nuclear energy, biomass, and other renewable energy sources such as solar, wind, and geothermal, using a wide range of processes. One of these processes is called electrolysis, which splits water into hydrogen and oxygen using electricity from multiple energy resources. The hydrogen can be stored, distributed, and used as a feedstock for transportation (trucks, rail, marine, etc.), stationary power, process or building heat, and industrial and manufacturing sectors (such as steel manufacturing), creating an additional revenue stream and increased economic value. Fuel cells generate electricity through an electrochemical reaction and can use different fuels. When using hydrogen as the fuel, they emit only water and heat. As long as there is a constant source of fuel and oxygen, fuel cells will continue to generate power. There is increasing interest in hydrogen and fuel cells from the rail, truck, and maritime sectors. This is shown through the rollout of the first hydrogen fuel cell train and hydrogen-powered boat. In addition, fuel cell delivery and parcel trucks are starting to deliver in California and New York, the world’s first fuel cell for marine ports was installed in Hawaii, and a heavy-duty fuel cell drayage truck demonstration is underway at the Port of Long Beach. The author believes in the relative long-term merits of FCEVs—which will offer the best value and lower risks long-term when considering:

• total-cost-of-ownership economics

• vehicle performance

• refuelling/recharging time

• supply chain risks

• geopolitical risks

• wells-to-wheels environmental benefits

• labour reallocation as we transition away from ICE-based locomotives.

National leaders are urged to give the Hydrogen and Fuel Cells a high priority on bringing hydrogen and fuel cells into full commercial use. This clean energy technology must be a critical part of the “New Energy Economy” that will become a legacy of our time.

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Hydrogen fuel cell design employs catalyst layers coated on either side of a proton-exchange membrane (PEM), to catalyse the desired oxygen reduction and hydrogen oxidation reactions at the cathode and anode, respectively. The catalyst coated membrane is further sandwiched between two carbon paper-based gas diffusion layers (GDLs) to create the membrane electrode assembly (MEA), which is then placed between bipolar plates and gaskets to form one fuel cell, within a stack of multiple cells.

1.1 HYDROGEN FUEL CELL ENERGY

A fuel cell is a device that generates electricity by a chemical reaction. Every fuel cell has two electrodes called, the anode and cathode.

The purpose of a fuel cell is to produce an electrical current that can be directed outside the cell to power electric traction motors. When using hydrogen as the fuel, the fuel cell emits only water and heat. As long as there is a constant source of fuel and oxygen, fuel cells will continue to generate power.

Figure 2 Stacked Fuel cell

Every fuel cell also has an electrolyte, which carries electrically charged particles from one electrode to the other, and a catalyst, which speeds the reactions at the electrodes.

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Figure 3 Fuel cell principle

Hydrogen is the basic fuel, but fuel cells also require oxygen. One great appeal of fuel cells is that they generate electricity with very little pollution- much of the hydrogen and oxygen used in generating electricity ultimately combine to form a harmless by-product, namely water.

The following circuit in figure 4 on page 8 is the proposed Traction Simulator that will be used to prove the operating system. Locomotives offer certain use cases where the:

1. fuel cell value proposition is strongest.

2. barriers to hydrogen refuelling are lowest.

3. decarbonization benefits from hydrogen fuel cells are disproportionately powerful.

In heavy-duty mobility, there are many use cases where fuel cells provide a number of key benefits, including:

• zero tailpipe emissions

• low noise and vibration

• fast and smooth acceleration

• a wide range of operating conditions with no compromise on vehicle payload

Fuel cells also provide additional benefits of long range, fast refuelling and full route flexibility, consistent with legacy diesel experience. Shunting locomotives present the lowest barriers to entry on hydrogen refuelling. That is because these vehicles typically return back to base each night and can be quickly refuelled at a centralized hydrogen refuelling station at their depot.

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Hydrogen can power fuel cell electric cars, trucks, buses and trains. The advantages of hydrogen powered vehicles compared to battery electric vehicles are faster refuelling times and the ability to travel longer distances carrying larger loads before refuelling. Refuelling hydrogen vehicles requires a network of refuelling stations, similar to what exists for petrol and diesel. Hydrogen fuel cells convert chemical energy into electrical power by combining hydrogen and oxygen with the aid of catalysts. As the only by-product of the reaction is water, they provide an efficient and environmentally friendly power source. Platinum is the most widely used catalyst for these fuel cells, but its high cost is a big problem for the commercialisation of hydrogen fuel cells.

To address this issue, commercial catalysts are typically made by decorating tiny nanoparticles of platinum onto a cheaper carbon support; however, the poor durability of the material greatly reduces the lifetime of current fuel cells. As noted by UCL Professor Dan Brett, a big barrier to the widespread commercialisation of hydrogen fuel cells is “the ability for catalysts to withstand extensive cycling required for their use in energy applications”.

Previous research has suggested that graphene — made from a single layer of carbon atoms arranged in a hexagonal lattice — could be an ideal support material for fuel cells due to its corrosion resistance, high surface area and high conductivity.

1.2 Hybrid Operation We also see opportunities for hydrogen refuelling corridors with high utilization to enable long-haul locomotive cases. Notably the cost for delivered hydrogen ($/ kg) reaches parity with diesel with scaled infrastructure and high utilization. There would also be no reason why long-haul locomotives trail their own tender with hydrogen. Afterall, steam engines had to trail their tender with coal fuel and that was never a problem. These additional benefits effectively address the limitations of stand-alone battery electric solutions that are range-constrained, require long recharge times with recharging infrastructure, and may be limited to certain routes. The author is promoting a hybrid locomotive that also uses batteries that are charged by regeneration when the locomotive is slowing down, travelling downhill or stopping.

Fuel Cells are solid state devices with no moving parts. A shunting locomotive is relatively low-powered with high torque required for:

• assembling trains ready for a road locomotive to take over,

• disassembling a train that has been brought in, and

• generally moving rail cars around the yard.

The three zero-emission propulsion options are electric, battery and hydrogen fuel cell. In this study batteries are combined with fuel cells but the batteries are there to support the auxiliaries on a locomotive. The system shows that the output of the fuel cells also charges the batteries.

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Strong Value Proposition In medium and heavy-duty mobility, there are many use cases where fuel cells provide a number of key benefits, including:

• zero tailpipe emissions • low noise and vibration • fast and smooth acceleration • a wide range of operating conditions with no compromise on vehicle payload

Fuel cells generate electricity from hydrogen and the emissions generated are water vapour and heat. The electricity is stored in batteries or fed directly into a locomotive’s high voltage propulsion systems. The shunting locomotives will be refuelled with hydrogen using on-site refilling stations – the only additional infrastructure element needed. To help tackle climate change and improve air quality in our communities, rail yards must switch to zero-emission solutions. Hydrogen powered trains are the most viable shunting option from both an operational and financial standpoint. Direct Torque Control (DTC) traction inverters will be used for traction which control the quadrature component of the stator flux relative to the rotor flux. DTC is explained later in this thesis. DTC has an advantage at low loads and gives excellent dynamic performance. Each inverter will receive input power from an Active Front End Inverter (AFEI) that will produce a constant 650 Vdc when power is received from hydrogen fuel cells. Each axle will be individually powered by a 3-phase permanent magnet AC motor. One of the aims of this work is to reduce slip and slide and improve tractive effort on the rail as well as introduce hybrid operation. The wheels all have a common denominator – the railway line. Like a car, the existing front wheels on a locomotive wear faster than the back wheels simply because a degree of the weight is transferred to the back bogie during traction and acceleration. There is an option that the locomotives can be connected to the shore supply when not in constant use. This will mean that the batteries will be fully charged through the intelligent battery charger to 650 Vdc when the locomotive is not in use. See section 4. When the locomotive is first set in action, it will be powered from the battery supply until the battery voltage drops to a predetermined level, probably 590 Vdc. At that point the hydrogen fuel cells will be connected automatically by the system. The traction inverters will receive power from the active front end inverters providing 600 V to the input of each traction inverter. At the same time the batteries are charged according to the IUIU algorithm discussed in section 4.1 The following figure 4 is used later in this thesis related to Slip/Slide control.

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Figure 4 Hybrid Circuit Diagram

HOW FUEL CELLS WORK

Fuel cells work like batteries, but they do not run down or need recharging. They produce electricity and heat as long as fuel is supplied. A fuel cell consists of two electrodes—a negative electrode (or anode) and a positive electrode (or cathode)—sandwiched around an electrolyte. A fuel, such as hydrogen, is fed to the anode, and air is fed to the cathode. In a hydrogen fuel cell, a catalyst at the anode separates hydrogen molecules into protons and electrons, which take different paths to the cathode. The electrons go through an external circuit, creating a flow of electricity. The protons migrate through the electrolyte to the cathode, where they unite with oxygen and the electrons to produce water and heat.

FUEL CELL STACK

The fuel cell stack is the heart of a fuel cell power system. It generates electricity in the form of direct current (DC) from electro-chemical reactions that take place in the fuel cell. A single fuel cell produces less than 1 V, which is insufficient for most applications. Therefore, individual fuel cells are typically combined in series into a fuel cell stack. A typical fuel cell stack may consist of many fuel cells. The amount of power produced by a fuel cell depends upon several factors, such as fuel cell type, cell size, the temperature at which it operates, and the pressure of the gases supplied to the cell.

The fuel processor converts fuel into a form usable by the fuel cell. Depending on the fuel and type of fuel cell, the fuel processor can be a simple sorbent bed to remove impurities, or a combination of multiple reactors and sorbents.

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Polymer electrolyte membrane (PEM) fuel cells are the current focus of research for fuel cell vehicle applications. PEM fuel cells are made from several layers of different materials. The main parts of a PEM fuel cell are described below. The heart of a PEM fuel cell is the membrane electrode assembly (MEA), which includes the membrane, the catalyst layers, and gas fusion layers (GDLs).

Hardware components used to incorporate an MEA into a fuel cell include gaskets, which provide a seal around the MEA to prevent leakage of gases, and bipolar plates, which are used to assemble individual PEM fuel cells into a fuel cell stack and provide channels for the gaseous fuel and air.

MEMBRANE ELECTRODE ASSEMBLY

The membrane, catalyst layers (anode and cathode), and diffusion media together form the membrane electrode assembly (MEA) of a PEM fuel cell.

POLYMER ELECTROLYTE MEMBRANE

The polymer electrolyte membrane, or PEM (also called a proton exchange membrane)—a specially treated material that looks something like ordinary kitchen plastic wrap—conducts only positively charged ions and blocks the electrons. The PEM is the key to the fuel cell technology; it must permit only the necessary ions to pass between the anode and cathode. Other substances passing through the electrolyte would disrupt the chemical reaction. For transportation applications, the membrane is very thin—in some cases under 20 microns.

CATALYST LAYERS

A layer of catalyst is added on both sides of the membrane—the anode layer on one side and the cathode layer on the other. Conventional catalyst layers include nanometre-sized particles of platinum dispersed on a high-surface-area carbon support. This supported platinum catalyst is mixed with an ion-conducting polymer (ionomer) and sandwiched between the membrane and the GDLs. On the anode side, the platinum catalyst enables hydrogen molecules to be split into protons and electrons. On the cathode side, the platinum catalyst enables oxygen reduction by reacting with the protons generated by the anode, producing water. The ionomer mixed into the catalyst layers allows the protons to travel through these layers.

GAS DIFFUSION LAYERS

The GDLs sit outside the catalyst layers and facilitate transport of reactants into the catalyst layer, as well as removal of product water. Each GDL is typically composed of a sheet of carbon paper in which the carbon fibres are partially coated with polytetrafluoroethylene (PTFE). Gases diffuse rapidly through the pores in the GDL. These pores are kept open by the hydrophobic PTFE, which prevents excessive water build-up. In many cases, the inner surface of the GDL is coated with a thin layer of high-surface-area carbon mixed with PTFE, called the microporous layer. The microporous layer can help adjust the balance between water retention (needed to maintain membrane conductivity) and water release (needed to keep the pores open so hydrogen and oxygen can diffuse into the electrodes).

BIPOLAR PLATES

Each individual MEA produces less than 1 V under typical operating conditions, but the locomotive application require a higher voltage. Therefore, multiple MEAs are connected in series by stacking them on top of each other to provide a usable output voltage. Each cell in the stack is sandwiched between two bipolar plates to separate it from neighbouring cells. These plates, which may be made of metal, carbon, or composites, provide electrical

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conduction between cells, as well as providing physical strength to the stack. The surfaces of the plates typically contain a “flow field,” which is a set of channels machined or stamped into the plate to allow gases to flow over the MEA. Additional channels inside each plate may be used to circulate a liquid coolant.

Conclusion: Hydrogen Storage for renewable Energy Systems by Even Grey of Griffith University

•Gaseous, liquid, “chemical” and solid-state hydrogen storage each has its place in energy storage and distribution

•For vehicles, high-pressure gaseous storage is the present reality, but the volumetric energy density is poor and unlikely to improve much

•Liquid hydrogen, ammonia, organic liquids and compressed gas are all contenders for large-scale storage and export

•Solid-state storage at the 1000 kg H2level is a (bespoke) commercial reality

•Solid-state storage is a good choice for small stationary systems because of the low pressure, high volumetric energy density and cost-competitiveness with batteries over the system lifetime In countries where passenger trains are less popular, like the US, the ability to convert freight trains to hydrogen power will be key to making the case for mass producing them. A recent report sponsored by the US Energy Department and Federal Rail Administration notes that while powering freight trains with hydrogen is more technically challenging, it would ultimately have “the highest societal value”. Freight is, however, heavier than passengers, so it would require more hydrogen, or more efficiently compressed hydrogen, to carry the same load the same distance that diesel-fuelled freight trains currently manage.

More countries are considering adopting the right to a healthy environment soon, either in their constitutions or general legislation, including Algeria, The Gambia, Chile, Canada and Scotland. But some of the world's richest – like the UK, United States, China and Japan – have yet to officially consider it. Meanwhile, Boyd still advocates for recognition at the UN level, which could compel more countries to recognise and strengthen it and create ways of holding countries accountable on the international stage.

Smarter, cleaner, quieter Hydrogen trains should be driven by efficient electric

motors powered by high-output hydrogen fuel cells. Besides being a proven alternative to diesel combustion engines, hydrogen fuel–powered trains offer:

• Reduced noise and vibration

• Fast refuelling, with less than 20 minutes of downtime

• 18+ hours of operation between fuelling

• The ability to turn existing non-electrified railway lines into zero-emission lines without

costly long-range electrification infrastructure

• Lower maintenance and operating expenditures

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SYNOPSIS 2: Slip/Slide Control A traction control system which measures the relative circumferential wheel speed difference of each axle with respect to the chosen master axle. This information is instantaneously recorded each time the locomotive is coasting on no-load in either direction. In the forward direction the back wheels set is the master. In the reverse direction the front wheel set is switched to be the master. The circumferential speed of each wheel axle is recorded via a resolver attached to the non-drive end of each traction motor. The speed difference of each axle is due to the variations in wheel circumferences. This information is sent to a master controller which calculates the torque to be applied to each traction motor so that all motors provide equal adhesion to the rail. This corrective torque signal is integrated with the traction inverter software to correct the torque of each ac traction motor for both slip (traction) and slide (braking) conditions. In this way, different torque is applied to each axle thus compensating for differences in wheel circumferences. The purpose is to reduce wheel wear and to maintain maximum adhesion from a new wheel (larger circumference) to a fully worn wheel (smaller circumference). Most important is to prevent flats on wheels caused by braking.

Schaffler Consulting principle is PREDICTIVE. It was challenged by GE but they failed. GE system is RESPONSIVE and failed to challenge this patent.

2.1 PRIOR ART FOR SLIP/SLIDE CONTROL The locomotive control system calculates the reference based on the common locomotive speed to produce a torque reference for the traction control system. Wheel wear on a locomotive is significant. Depending on the position of the wheel, wear varies between the front and rear wheels resulting in differences in wheel diameter. If the same torque reference signal is sent to each traction inverter, the tractive force on each wheel will depend on that particular wheel diameter. Therefore, different diameter wheels will create different torques at the wheel / rail connecting surface. This difference will initiate slide on the smallest diameter wheel. The electrical traction system must not use one common inverter to drive all the traction motors on a bogie, the result will become worse because all the traction motors will apply the same torque to wheel axle but will result in varying adhesion where the wheel diameters are a major factor. It must be understood that on a locomotive the left and right wheels are solidly attached to a common axle. For the same torque, the wheel with bigger diameter will have less force delivered, which will cause less adhesion. Conversely, the wheel with smaller diameter will deliver higher force, which increases the risk of slipping. The converse applies during braking where slide is a major cause of wheel flats and wheel wear. The attached diagrams show below the typical locomotive wheels in the way that wear takes place.

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CO-CO locomotive with 6 axles

Equal Wheel Diameter = Equal Torque

Smaller Wheel Diameter (e.g. worn out) = Torque Adjustment needed to avoid slip (in traction) and

slide (in braking) to maintain equal adhesion

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In present practice this is what is experienced. Locomotives need to be taken out of service every three years to replace the wheels on each bogie set. It is expected that this service requirement will increase to 10 years using this Slip/Slide proposed system. In this development the master reference is taken from the back wheel when in traction when off load and moving forward. The back wheel is least likely to slip. The master / feedback notation is reversed when the locomotive travels in the reverse direction. Loco’s can typically be used for multiple purpose – one day hauling Freight, the next Passenger – in Australia the only Loco-hauled passenger services left is The Indian Pacific and the Ghan – just about all the rest are becoming Multiple Unit or dedicate Push-Pull power cars. On multiple unit trains the wheel tread wear is minimal – about the only cars that show tread hollowing on in Australia were the Broadmeadow Endeavour fleet – and that was because they didn’t suffer flange wear due to the very gentle curves they encountered – takes several years to get to 2 mm of tread hollowing, at which point a very rough riding is experienced due to hunting, having lost the normal conicity off the wheel tread. i.e. At a maximum up to 4 mm wear off the diameter on the tread-line. Locomotives typically still have Cast Iron brake blocks which helps adhesion, so could help to address tread hollowing. It is possible to see more wear off the diameter on a Locomotive, but flange wear on a tri-axle bogie is a bigger issue. During braking, the axle will first ‘creep’, on the way to complete sliding. Reduction in braking force must occur during the creep phase in order to prevent damaging lockups (i.e. flat-spotting). High enough creep differential will cause wheel burns (similar to wheel-spinning). A small amount of creep (in either traction or braking) will cause an increase in adhesion (this is the stable zone), but at some point it becomes unstable, the axle speed rapidly breaks-away and adhesion reduces (at which point the WSS/WSP must reduce the tractive/braking force quickly enough to get it back into the stable zone). The fastest or slowest axle (depending on braking or traction) provides the reference - the difficulty then comes if all axles creep together. At this point angular acceleration limits are used by WSP systems to determine that the axles are starting to be spinning/sliding. The leading axle potentially sees the lowest adhesion, but in practise this is not necessarily the case – the adhesion difference between one axle to the next is also generally negligible. Load shift does occur from front to back between bogies and within bogies, especially as the brakes are beginning to apply. The wheel loading across all wheels is also not identical and changes dynamically – thus we see different axles locking up from time to time (not always the same one first). Wheels also pick-up varying contamination from Gauge Face Lubricators and from Top Of Rail Friction Modifier Applicators, another significant source of variability between axles. Locomotives can dispense sand ahead of each wheel to improve adhesion – obviously this depends on the system working properly and sanding works best at low speed (at high speed you need a much high sand flow rate as so much is being blown away). The latest EMU’s provide Regenerative power back into the OHW and have full Rheostatic brake resistors for when the overhead is non-receptive. All modern loco’s use Dynamic (Rheostatic) braking when coming down the grades.

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Examples: It is important that the system is not just slide avoidance – it must be slide control. For example, the Alstom AC traction system wheel slip/slide control on Millennium is found to be disappointing – under Electro-Dynamic braking the performance under low adhesion conditions was poor compared to the friction only performance (under pneumatic WSP control) – so much so that we configured the system to abandon ED braking altogether if the traction system detects slide continuously for only 0.9 sec. The Mitsubishi traction wheel slip/spin control on OSC has been found to be equivalent to that of the pneumatic brake WSP system and similarly that of the Hitachi Traction on Waratah. Lowest adhesion under braking seen since Event Recorders were installed has been 2.5%, for an 8-car Tangara Australian passenger train. The WSP system prevented slide damage to any wheels during that incident, but the catchpoint could not be stopped. Typically expected is >15% adhesion for dry track and 8-12% adhesion for wet track. DDIC’s with everything working need 6% to get up the Blue Mountains. There was one occasion where this was not achieved (obviously momentum can get them through small patches of <6%). Waratah’s are designed for 22% adhesion under power and 18% adhesion under ED though it is programmed to drop the ED targets should wheel slip continues. DC locomotives with good traction control achieve around 30% adhesion, whereas the latest AC locomotives were achieving around 35% - this is with water-spraying fitted for testing.

2.2 BACKGROUND OF TRACTION CONTROL In principle, existing locomotives with AC traction motors on each axle each driven by an inverter generates torque reference according to the information of throttle position placed there by the driver. The inverter control system generates PWM signal to fire switching devices according the torque requirement, the inverter produces the power to drive the traction motor. Such system does not provide compensation differences in wheel diameter. This applies particularly to direct diesel driven wheels. Note that thyristor controlled DC traction is not even considered in this report as it is inefficient and totally out of date. In practice, it is the front wheel axles that is most likely to slip simply because the weight is transferred to the back axles so they are not likely to slip. The weight is lifted off the front axle to a degree so that axle is the most likely to slip – and they do slip. The proposed main traction inverter system will be connected to the traction control system via serial bus. The traction control system deals with slip/slide control on each individual wheel providing wheel diameter compensation.

The following are tasks managed by the traction control system:

• Main traction inverter control and protection logic

• Lower level traction and braking characteristic maximum limitation

• Traction effort and braking acceleration and de-acceleration limitation

• Life guarding signal monitor

• Fault and operation information transmission

• Slip/Slide control and protection logic

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2.3 Functionality of Locomotive wheel Slip/slide control with predictive wheel diameter using AC 3-phase AC traction

1. To begin with, it is assumed that the locomotive starts from standstill without any load connected. The first function is to calibrate the traction wheels and store the wheel circumferences in the Master Control System. This calibration should take place on a regular basis but not when a load is attached to the locomotive.

2. Reference must be given to the traction inverters so power is applied to the traction

motors in proportion to the circumference of each wheels simultaneously. Currents will be drawn for each reaction motor according to the wheel circumference.

3. The moment the locomotive moves, the Master Control System will measure and record the speed of each wheel from the resolver attached to the non-drive end of each traction motor and store this information.

4. The master resolver is allocated to the traction motor on the back-wheel axle of the

locomotive when travelling forward but it must be switched to the traction motor on the front wheel axle when travelling in reverse.

5. The reference from the driver’s speed lever should match the speed recorded from the

master resolver. It is to be expected that with a load of trucks attached to the locomotive, the traction motors will be operating in accordance with the wheel circumference.

6. If the speed of any wheel increases above the master speed, the inverter must immediately reduce the reference to that inverter to slow that wheel back in line with the master wheel.

7. If all wheels are slipping due to excess acceleration, that will be sensed by a reduction in load current and the speed to all traction inverters must be reduced. This indicates that the accelerating current setting is too high and must be reduced due to total slippage. This can be caused by water or oil on the track.

8. When the driver’s lever requires a reduced speed, the inverters will regenerate power that is used for charging the batteries. This energy can also be used in dynamic braking. This would be more applicable to long haul traction.

9. When the locomotive is in the braking mode, the master must be switched to the front wheels since trucks pushing behind will cause the back of the loco to rise slightly and therefore reduce the pressure on the back wheels.

10. Reference is made here to the NYAB system designed and supplied by the author. See page 49 where the description is given. In practice, the wagons will cause a traction behind the locomotive and the behaviour is not expected to lift and reduce the pressure on the back wheels of the locomotive. This issue will need to be settled in practice with the drivers.

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2.4 SUMMARY OF THE SLIP/SLIDE INVENTION This current invention provides a new means to compensate for the force difference on each wheel caused by wheel wear. It must be understood that when addressing the issue of wheel diameter on rolling stock, there are always two wheels rigidly linked together, left and right, by a solid axle. The control system will learn the speed of each wheel when the locomotive is coasting or at a pre-defined interval time, according the speed feedback. This is calibration that can be automatically recorded when the locomotive is off load. The back axle is assumed as the master. However, in reverse, the front axle is switched to be master. A compensating coefficient is then calculated for each axle. The respective compensation coefficient is applied to each traction inverter, which causes each traction motor to deliver the same effort at the rail contact as accurately as possible thus taking into account the wheel diameter. At the same time the conditions of the rail are considered for sand, water, oil and ice. In the locomotive where the invention will be used, each traction motor will be driven by a separate dedicated inverter - direct torque converter (DTC). This will provide improved adhesion utility because each traction motor will deliver the correct force for the track condition. It is important to note that although new locomotives claim to have slip/slide control, they make no allowance for change in individual wheel diameter. The phenomenon of slip is closely related to the adhesion effort. Because in the end the objective of a re-adhesion control is to keep an optimal wheel slip. To design this control system, the adhesion characteristics must be considered as precisely as possible. However, in practice it is impossible to know the exact condition of the wheel-rail surface and whether the locomotive is in traction of braking. The fundamental relationship between adhesion and wheel slip under different rail and wheel conditions can be explained in the figure below. The adhesion-slip characteristics can be divided into a stable and unstable region. In the unstable region more wheel slip occurs, the less adhesion results. To maximize the adhesion effort a re-adhesion system needs to be constantly in control of slip so that the adhesion coefficient between the wheel and the rail is near the top of the initial positive slope of the adhesion-slip curve. See figure 20, page 39.

Tractive Effort = Weight on the drivers x Adhesion Adhesion = Coefficient of Friction x locomotive adhesion variable Tractive Effort = Weight on drivers x Coefficient of Friction x locomotive adhesion variable Locomotive adhesion variable is the factor that needs to be controlled by the traction inverters. Coefficient of Friction between the wheel and rail is usually between 0.40 and .045 for relatively clean and dry conditions. Typical damage caused by wheel slip is illustrated in the picture below where the locomotive was unable to get it load of wagons away. The front bogie wheels slipped and the back-bogie

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wheels were helpless to pull the load away. A typical rail disaster is shown below where the bogie wheels slipped severely so that the locomotive was unable to pull the load.

The figure 5 below shows the traction arrangement on a locomotive. The motor is suspended on the axle and drives through a pinion gear on to the main reduction gear wheel. It is necessary that an encoder be fitted to the non-drive end of the motor to sense the proportional speed of the railway wheel. In practice the encoder will be fitted within the motor enclosure so as to protect it from early destruction.

Figure 5

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2.5 BRIEF DESCRIPTION OF THE DRAWINGS USED The next drawing figures 6 and 7 shows how the adhesion coefficient system for different track conditions.

Figure 6

Then drawing figure 7 shows the how the traction inverter and motor will be connected in the locomotive.

Figure 7

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The tractive effort delivered by each traction motor is determined by the following equation: F = (2 * T * η * r ) / D Where: T – Torque of the traction motor η – Gear efficiency r – Gear Ratio D – Wheel Diameter Factors that are fixed by the design of the locomotive are:

• Traction motor torque, therefore there is no correction made for reduced wheel diameter.

• Gear ratio and the gear efficiency. Factors that are not fixed are:

• Wheel diameter changes as the wheel wears. The greatest wear is usually on the leading wheels on the leading bogie. The least wear is on the back wheel of the trailing bogie.

• Diameters will be the same when the locomotive is new but they change rapidly with

use. Wheel diameters can vary by 25 mm in diameter from one axle to another.

2.6 THE INVENTION This invention provides a means to compensate the force difference at each wheel according the difference in wheel diameter.

CLAIMS What is claimed is: 1) The system function description of the traction control system which will

communicate with the traction inverters; 2) The system description whereby the tractive force applied by each motor is a function of wheel diameter; 3) The tractive effort compensation method which has been provided in the summary of the

invention 4) The master reference is dependent on the direction of the locomotive and the state of slip

or slide. 5) The locomotive system structure related with this invention. By predicting wheel diameter, we will prevent slip or slide and therefore provide an improved adhesion so that a larger load can be hauled by each locomotive regardless of wheel wear.

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2.7 PREDICTIVE TOPOLOGY Predictive technology works by measuring the diameter of the wheel. There are two variables: Slipping Force and Diameter We know the force and the diameter therefore we can calculate the point at which the wheels will slip and so we can predict the point at which the wheel will slip. Weather conditions are sensed by motor current measurement

- Slipping force => friction - Diameter From these two parameters we can predict when slip occurs.

CONTINUED WORK

The present invention relates to improving track adhesion in electric propulsion of a locomotive travelling on steel rails. Vehicles on rails obtain their traction and braking forces by means of friction between the wheel surface and the rail surface. In a conventional vehicle, slip and slide occur when the forces applied to the wheel are larger than the maximum friction force between the wheel and rail surfaces. Slip occurs when forward torque is applied to the wheels. Slide occurs when a braking force in the shape of reverse torque is applied to the wheels. This invention presents a way to predict and minimize the occurrence of slip and slide based on wheel diameter, thus improving vehicle adhesion. There is a low margin in the value at which optimum tractive effort is realised, known as optimum creep. Optimum creep depends on track surface conditions, wheel circumference and vehicle speed. The power torque signal that is applied to the propulsion system is reduced when slip or slide occur as a result of track condition and vehicle speed. In conventional systems the same torque reference signal is sent to each traction converter, thus ignoring differences in wheel circumference. This proposed design is expected to closely perfect the degree of slip and slide. Differences in wheel circumference due to wear cause variations in the optimum creep value at the wheel to rail surface. When the same torque is applied to the axles, the wheels with a bigger diameter will exert less traction force. In contrast, the wheels with a smaller diameter will exert a higher traction force to the rail surface thereby increasing the occurrences of slip and slide. The researched system compensates for differences in wheel diameter. Differences in wheel wear in electric propulsion vehicles are significant. Wheels do not naturally wear by the same margin. Wheel wear varies considerably depending on the location of a wheel on the vehicle, direction of travel and vehicle loading. Slip and slide are more likely to occur on wheels that are worn and thus have a smaller diameter than other wheels on the vehicle due to the small margin at which optimum creep is obtained. The same applies during braking where slide aggravates wheel flats and wheel wear. Accordingly, the tractive force exerted by the wheel surface on the rail surface depends on the wheel diameter. This difference will initiate slide on the smallest diameter wheel. A 10% decrease in wheel diameter has resulted in a tractive force increase of 11.5% on that wheel. Worst of all is when a wheel slides and creates a flat on the wheel. In this case the wheel has to be replaced immediately. The angular velocity of a wheel is directly related to the circumference of that particular wheel. Wheel diameter varies considerably due to wear with age and location within the bogie. An

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object of the present invention is to provide a traction control system that improves the adhesion characteristics of electric locomotives by accurately measuring differences in angular velocity of individual axles. This will determine wheel circumference and incorporating the parameters thus obtained in the traction control loop, thus decreasing the traction force in axle assemblies that have smaller wheels by a fraction that is equivalent to the difference in tractive force. The torque power generating means consists of a master controller that receives the angular velocity of each driven axle, controlling a plurality of traction inverter circuits that drive a plurality electric motors applying torque to the axles. In a first embodiment, each axle assembly consists typically of:

• an axle solidly connected to two wheels,

• a Permanent Magnet 3-phase AC traction motor

• a resolver direct mounted to the traction motor, coupled to provide feedback to the

Master Controller

• a DTC traction inverter coupled to the Master Controller.

The vehicle typically includes a plurality of axle assemblies, usually two or three axles per bogie as well as a primary energy source a means for controlling the primary energy source and energy conversion means such as a Hydrogen fuel cell. The proposed design is intended to use an active front end inverter to accept the dc voltage from the fuel cells and provide a fixed 650 Vdc to the traction inverters and auxiliaries. The auxiliaries do not form part of the development because they are already operating and designed by the author. A master control circuit receives input from a plurality of resolver devices to determine the angular velocity of each axle. Angular velocity is directly related to the circumference of wheels that are mounted on each axle. The master control circuit compares the angular velocity of each axle and adjusts the traction inverter speed output on the axle assembly to compensate for wheel wear, resulting in the same torque at the wheel to rail surface for all wheels on the vehicle. Most buyers of locomotives still choose DC traction worldwide because they are more familiar with the operation even though it has poor efficiency and significant service required. Locomotives using diesel driven alternators and DC traction are inefficient and create significant carbon emission. It is the intention to produce a more efficient ac locomotive. Hydrogen fuel cells will provide zero emission. By predicting the required torque for an existing wheel diameter so that adhesion can be maintained throughout the useful life of a traction wheel. There is a definite need for hybrid ac traction on locomotives. We are developing traction inverters for locomotives. The system of "Slip /slide with wheel diameter compensation". A major problem that any rail traction system has is slip during traction and slide during braking particularly when the 6 axle wheels are worn to different sizes. Bernard Schaffler has patented their slip / slide system with wheel diameter compensation.

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2.8 CALIBRATION This can take place automatically whenever the locomotive is operating off load and below 10 kph. However, depending on conditions it can be arranged so that the driver of the locomotive presses a calibration button at a time and place more convenient for the existing conditions of that locomotive. At that point the reading will be read from each encoder and stored in the system. Each encoder will be compared against the master which is the leading axle. Any variation in speed of any following wheel will cause an adjustment in speed of the axle. Locomotives with four axles (two per bogie) are mainly for shunting and are called BO_BO Locomotives with 6 axles are for main line haulage and are called CO_CO Locomotives with 8 axles are for main line haulage (mainly used in South America) and are called DO_DO. The intention is to prove the principal by using what has been labelled “The Traction Simulator Unit” as illustrated above in figure 8. The gearboxes are helical spur and definitely not worm boxes.

• The large wheels solidly connected by an axle represent the railway line and are driven

by a separate variable speed inverter system.

• The left auxiliary wheel represents the master.

• The opposite wheels are the slave and can be adjusted to run at different diameters of

the large railway wheel.

• The object of the system is to prove that the slave will adjust automatically so that

there is no slip during acceleration or constant speed or slide during deceleration

• Similarly, as the slave wheel becomes worn with a reduced diameter, the speed of that

traction wheel will increase automatically.

It is recommended that inverters for AC traction should use Direct Torque Control (DTC) to

achieve the best results in variable speed traction.

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2.9 TRACTION SIMULATOR UNIT

Figure 8

Tests will be conducted by pouring water, oil and sand grit on the main railway wheels to replicate the rail conditions.

3.1 DIRECT TORQUE CONTROL (DTC)

DTC is ideal for conditions required to power a locomotive where accurate torque control is required from standstill and creep speed.

It is recommended that inverters for ac traction on locomotives should use Direct Torque Control (DTC) to achieve the best results in variable speed traction. Three phase inverters used in traction application for torque and speed control of AC electric motors get the best results using Direct Torque Control (DTC). This requires calculating an estimate of the motor’s magnetic flux and torque based on the measured voltage and current of the motor. DTC is ideal for the conditions required to power an electric locomotive where accurate torque control is required from standstill and creep speed control is necessary.

Figure 9

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3.2 DTC Control Topology

• Stator flux linkage is estimated by integrating the stator voltages. • Torque is estimated as a cross product of estimated stator flux linkage vector and

measured motor current vector. The estimated flux magnitude and torque are then compared with their reference values. If either the estimated flux or torque deviates too far from the reference tolerance, the IGBTs of the variable frequency drive are turned off and on in such a way that the flux and torque errors will return in their tolerant bands as fast as possible. Thus, direct torque control is a form of the hysteresis. The properties of DTC can be characterized as follows:

• Torque and flux can be changed very fast by changing the references.

• High efficiency & low losses - switching losses are minimized because the IGBTs are switched only when it is needed to keep torque and flux within their hysteresis bands.

• The step response has no overshoot.

• No coordinate transforms are needed, all calculations are done in stationary coordinate

system.

• No separate modulator is needed, the hysteresis control defines the switch control signals directly.

• There are no PI current controllers. Thus, no tuning of the control is required.

• The switching frequency of the transistors is not constant. However, by controlling the

width of the tolerance bands the average switching frequency can be kept roughly at its reference value. This also keeps the current and torque ripple small. Thus, the torque and current ripple are of the same magnitude as with vector-controlled drives with the same switching frequency.

• Due to the hysteresis control the switching process is random by nature. Thus there are no peaks in the current spectrum. This further means that the audible noise of the machine is low.

• The intermediate DC circuit's voltage variation is automatically taken into account in the algorithm (in voltage integration). Thus, no problems exist due to dc voltage ripple (aliasing) or dc voltage transients.

• Synchronization to rotating machine is straightforward due to the fast control; Just

make the torque reference zero and start the inverter. The flux will be identified by the first current pulse.

• Digital control equipment has to be very fast in order to be able to prevent the flux and

torque from deviating far from the tolerance bands. Typically the control algorithm has to be performed with 10 - 30 microseconds or shorter intervals. However, the amount of calculations required is small due to the simplicity of the algorithm.

• The current measuring devices have to be high quality ones without noise because spikes in the measured signals easily cause erroneous control actions. Further

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complication is that no low-pass filtering can be used to remove noise because filtering causes delays in the resulting actual values that ruins the hysteresis control.

• The stator voltage measurements should have as low offset error as possible in order

to keep the flux estimation error down. For this reason, the stator voltages are usually estimated from the measured DC intermediate circuit voltage and the transistor control signals.

• In higher speeds the method is not sensitive to any motor parameters. However, at low speeds the error in stator resistance used in stator flux estimation becomes critical. Summarizing properties of DTC in comparison to Field-Oriented Control, (FOC) we have

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Comparison Property DTC FOC Dynamic response to torque Very fast Fast

Coordinates reference frame alpha, beta (stator) d, q (rotor)

Low speed (< 5% of nominal) behaviour

Requires speed sensor for continuous braking

Good with position or speed sensor

Controlled variables torque & stator flux rotor flux, torque current iq & rotor flux current id vector components

Steady-state torque/current/flux ripple & distortion

Low (requires high quality current sensors)

Low

Parameter sensitivity, sensor less

Stator resistance d, q inductances, rotor resistance

Parameter sensitivity, closed-loop

d, q inductances, flux (near zero speed only)

d, q inductances, rotor resistance

Rotor position measurement Not required Required (either sensor or estimation)

Current control Not required Required

PWM modulator Not required Required

Coordinate transformations Not required Required

Switching frequency Varies widely around average frequency

Constant

Switching losses Lower (requires high quality current sensors)

Low

Audible noise spread spectrum sizzling noise

constant frequency whistling noise

Control tuning loops speed (PID control) speed (PID control), rotor flux control (PI), id and iq current controls (PI)

Complexity/processing requirements

Lower Higher

Typical control cycle time 10-30 microseconds 100-500 microseconds

The direct torque method performs very well even without speed sensors. However, the flux estimation is usually based on the integration of the motor phase voltages. Due to the inevitable errors in the voltage measurement and stator resistance estimate the integrals tend to become erroneous at low speed. Thus, it is not possible to control the motor if the output frequency of the variable frequency drive is zero.

However, by careful design of the control system it is possible to have the minimum frequency in the range 0.5 Hz to 1 Hz that is enough to make possible to start an induction motor with full torque from a standstill situation. A reversal of the rotation direction is also possible if the speed is passing through the zero range rapidly enough to prevent excessive flux estimate deviation.

If continuous operation at low speeds including zero frequency operation is required, a speed or position sensor can be added to the DTC system. With the sensor, high accuracy of the torque and speed control can be maintained in the whole speed range.

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3.3 THE ACTIVE FRONT END INVERTER The AFEI will allow power to charge batteries through the intelligent battery charger when the locomotive is decelerating or travelling downhill. This fact improves efficiency that provides a saving in running cost. Details of Direct Traction Control are described in a section below in this thesis.

Figure 10

The circuit in figure 4 page 8 shows the proposed inverter traction system. A most important part is the output filter which is the common mode and differential mode filters. This filter will protect the traction motor bearings and winding insulation. This is a common motor failure when powered from PWM inverters due to the sharp rise time of the pulses. The pulses charge up the rotor and the only discharge path to earth is through the bearings so the bearings fail. The sharp rise in pulses will break down the insulation over three years. So often railway maintenance staff look for a better motor. What they really need is an inverter with common mode and differential mode filters. This was a problem that the author solved for New York Transit Authority who were looking for an improved motor because their motors only lasted 3 years. The author explained that they did not need a better motor but needed a better inverter with common mode and differential mode filters. This solved the problem for many hundreds of compressors drives on the main line rail cars. Large rectifiers generate significant harmonics back into the supply line. New regulations are intended to combat the use of uncontrolled rectifiers or line switching devices from being installed in new installations. Notwithstanding the future regulations, many organisations have had to take corrective action because the level of harmonics in their supply had become so intolerable causing interference and damage to electrical and mechanical plant. Typical power equipment which will be affected by the regulations will include:

thyristor converters used in DC drives thyristor battery chargers current fed inverters in UPS current fed inverters for motor control railway catenary supplies general high-power DC supplies.

The limits for harmonics are being imposed under IEC1000-3-6 in Europe and Australia and IEEE 519 in the USA.

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Damage Caused by Harmonics • Severely reduced power factor

• Overheating of AC induction motors

• Overheating of transformers

• Overheating of power factor capacitors

• Inaccuracy in instrumentation and control systems

• Synchronisation difficulties in line commutated power electronic products such as

inverters, soft starters etc.

• Harmonics voltages are passed on to all consumers sharing common feeder lines.

3.4 Basic Active Front End Inverter Scheme The basic converter scheme is shown in figure 4 on page 8 of this presentation. The input IGBT bridge and three phase reactor forms the power section of the Active Front End Inverter which is connected to the three phase utility supply so that it achieves the following objectives:

1. Minimise the harmonic distortion in the AC supply current. The Active Front End Inverter

removes all low frequency harmonics such as 3rd, 5th, 7th, 11th, etc. The harmonics generated by the Active Front End Inverter are confined to multiples of the switching frequency on the IGBT bridge which is 2 kHz.

2. Maintain a constant DC link voltage irrespective of the current absorbed or regenerated by the output inverter. The AC/DC/AC converter has the advantage of requiring a relatively small size of DC link capacitors which reduces costs and size of the equipment.

3. Maintain a power factor close to unity. This is a natural feature of the active front end inverter to keep the current in phase with the line voltages. Uncontrolled rectifiers will give a power factor from 0.5 to 0.72 depending on the line impedance and filter inductance.

4. Produce a DC supply which has four quadrant characteristics for regeneration of power back to the utility AC supply. The Active Front End Inverter has the advantage of providing this facility with only the use of uni-directional power devices.

3.5 Principle of Operation of the Active Front End Inverter The system circuit (figure 4) on page 8 is focussed on an AC/DC/AC converter. The Active Front End Inverter can be a stand-alone unit which can regenerate a DC source. It can also be a regulated DC supply. Although the circuit describes a 3-phase system, this is equally applicable to single phase systems as experienced from rail network supplies. The input converter consists of six switches (IGBTs). With appropriate sinusoidal PWM modulation, the AC/DC converter will control the phase and magnitude of the current so that it is in phase with the input supply voltage. This system of control produces near sinusoidal current at near unity power factor at the output of the AC/DC converter.

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Figure 11

The line reactor is an essential part of the Active Front End Inverter. Simulations enabled the choice of inductor to an optimum value of 15% of line reactance. At the moment when power is applied, the DC bus voltage reaches around 580 volts due to the full wave rectification. The diodes form the charging circuit for 200 milliseconds after which the IGBTs are gated on by the control system so that the DC bus climbs to 750 volts DC due to the boost action of the PWM bridge. As its name implies, the output voltage is boosted to a higher voltage than the diode rectified voltage. Referring to figure 12, the boost action operates as follows: Closing S1 causes the diode to be reverse biased isolating the output from the input. During this time the input supplies energy to the inductor. The boost action takes place when S1 is turned off since energy is received from the inductor as well as the input. By controlling the switching modulation in relation to the supply frequency, the DC bus can be controlled at a desired level.

figure 12

The output bridge feeding the load creates a fast dynamic responding sinusoidal output current to control the load at the desired voltage and frequency. The capacitor bank stores the right amount of energy so as to limit the transient ripple below a suitable limit. The ripple is caused by the unbalance in demand between the input and output power.

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3.6 CONTROL STRATEGY Current control is the key part of an active front end inverter. It achieves a fast response by using Predictive Current Control of the input line current. Ramp comparison modulation involves measuring the error between a target reference current and the actual output current, and using this error to change the PWM output voltage of the inverter. It offers the benefit of a fixed switching frequency, but has the disadvantages of needing to have the control loop accurately tuned to suit the load parameter, and having a steady state phase error between the target current and the output current. Predictive current control involves determining the correct inverter output voltage to achieve the desired target current in the next switching cycle and offer the potential for the best performance. This system is used in preference to Hysteresis Current Control. The advantages of the Predictive Current Controller over the conventional hysteresis current controller are:

1. The Predictive Current Controller is set at a constant switching frequency. It makes use of a lower switching frequency and therefore produces lower switching losses. This is particularly important for large power converters. The hysteresis current controller has an error band which sets up the upper and lower error boundaries. The frequency is therefore variable and uncontrollable as the current oscillates from the upper to the lower boundaries causing undefined losses. If the error band is reduced the switching frequency increases even more.

2. The Predictive Current Controller regulates the vector angle while the magnitude of

the vector is maintained constant. This increases the accuracy of current control which is important for large powers. The hysteresis current controller does not take into account the vector angle. It only regulates the amplitude of each individual phase current. It may fall into a so-called limited cycle which generates extremely high switching frequencies. This phenomenon is most undesirable in large converters.

3. In the predictive current controller, the three phases are treated as a whole rather

than separately as in the hysteresis method giving good overall control. Predictive current controller makes use of zero space vector to reduce the switching harmonics substantially.

4. To achieve the same accuracy the hysteresis current controller may require at least 10 kHz switching frequency whereas the predictive current controller requires less than 5 kHz.

3.7 Step changes to the Active Front End Inverter Two significant results are shown in the following figures relating to the output response of the Active Front End Inverter. Figure 13 and 14 relate to a 50% step change in line voltage at the 0.04 second point. The over shoot in bus voltage occurs for less than 10 milliseconds. Naturally the input current reduces for a given load because the voltage has been increased.

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Figure 13. AC load current displayed when a 50% increase is applied to the supply voltage.

Figure 14.

DC bus voltage displayed when a 50% increase is applied to the supply voltage. Figure 15 displays the AC load current and DC bus voltage on the same axes. At point 0.04 seconds when the load was applied, there is no noticeable change in the DC bus voltage. This is a good illustration of the point made previously on the fast response of the Predictive Current Controller.

Figure 15. AC Line current and DC bus voltage for a load increase from 50% to 100%.

Note: The initial transients in figure 13 are start-up transients as the Active Front End Inverter turns on an initially boost from the rectified 580 volts DC.

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3.8 Conclusion for Active Front End Inverter The above results show clearly that the Active Front End Inverter will solve many problems relating to power saving, removal of harmonics and allow the control of stable DC supplies particularly when regeneration occurs due to back emf caused by reactive systems. This a major step towards improving the electrical pollution which is rapidly destroying the utility networks throughout the world.

4 Locomotive Master Control System Refer to figure 4 at the beginning of this presentation The master control system will act as an interface between the driver and the traction inverters.

Calibration of each wheel diameter will take place automatically whenever the locomotive is off load and operating at about 10 kph. Each wheel is fitted with a resolver. The back axle is assumed the master when the locomotive is operating in the forward direction. In reverse the front axle will assume the master. The system will calculate the diameter of each wheel and correct the speed of each wheel through the traction inverter to match that of the master.

If the locomotive leaves without calibration then it will assume the wheel diameter recorded from the last journey. The traction inverters will switch individually at variable frequency which will allow instantaneous wheel speed correction. Flywheel action between each inverter and each motor will be set up so that if the locomotive has been coasting without power, the gate drive can be reapplied safely without causing an over current trip in the inverter due to an out-of-synchronous situation. The system will calculate the output effort required for each traction motor according to the driver’s lever notch position and the instantaneous individual wheel diameter.

The system will modify the torque reference received from the driver’s speed lever taking the current rail status, (dry, wet, sandy conditions) into consideration and then send a corrective torque reference to each inverter/motor. This will significantly reduce the possibility of traction motor over current trip when slip ceases abruptly. This is achieved using Cycle by Cycle Current Limiting at the switching frequency of the traction inverter. The system will control dynamic braking Active Front End inverter incorporated in the traction inverter to suit the needs for braking. This is the additional advantage of incorporating the Active Front End Inverter. When traction is in progress and before over voltage occurs, the system will gate the IGBT in a pre-defined method until the dc link voltage drops to a safe zone. When braking, the system will modulate the IGBT to maintain constant voltage dc link.

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Figure 16 Master Control System for the traction system.

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4.1 Battery Charging on a Locomotive

1. Batteries on a locomotive can be normal lead acid batteries. Weight is required to assist traction. It is still to be decided whether Lithium-ion batteries should be used. Recent batteries used on the London Underground were normal lead acid charged by a 135 kW battery charger.

2. Battery chargers will accept the variable voltage / variable frequency supply direct from the fuel cells. Many similar battery chargers designed by the author have been in operation for many years in many parts of the world. The battery charger will have the IUIU algorithm for charging and incorporate automatic maintenance functions such as equalising. See figure 11.

3. It is expected that from past experience the battery life will exceed 8 years using this algorithm.

4. Battery charging is not allowed from the regenerated link. Power for charging has to be powered to the input of the battery charger. Note power from the link is blocked through diodes.

5. Regenerated power will be used to drive the dynamic brake cooling system and auxiliary inverters and ac induction motors.

6. Dynamic braking will only be used when the locomotive needs speed reduction. Wherever possible the regenerated energy will be used to charge the high voltage batteries so that traction motors can be powered from 650 Vdc batteries. Auxiliary loads such as inverters driving radiator blowers and heat exchanger blowers will also use battery supply.

7. Dynamic braking will only actuate when the regenerative voltage from the traction inverters exceeds 700 Vdc because at that stage all auxiliaries and battery charging loads are already absorbing whatever they can and then whole train braking becomes necessary.

Figure 17

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5 WHEELS ON ROLLONG STOCK The surface of a rail wheel making rail contact is tapered so the diameter nearest the wheel flange is greater than the diameter on the outer edge of the wheel. See figure 18 below. When the locomotive travels on a bend to the left, the weight of the vehicle causes the body of the locomotive to move to the outer edge by centrifugal force so the largest wheel diameter on the right is in contact with the rail. The wheel on the left side moves to the outer diameter which is less than that of the right wheel. This ancient fact reduces wheel wear on track curves and allows rolling stock to travel on bends. The track dictates the maximum curve allowed. This will be dealt with by the traction algorithm. Queensland Rail use narrow gauge rail so the railway line can curve sharper than that in New South Wales where standard gauge is used. The natural hilly terrane of Queensland calls for narrow gauge to be used. Most of Australia use standard gauge at 1435 mm.

Figure 18

The picture shown of the railway line disaster earlier in this presentation is real and the aim of this development is to remove the possibility of such a disaster. A reliable senior rail engineer advises that all the locomotives owned by that rail company only measure wheel diameter after three years and in most cases the wheels in the front bogie have to be replaced. This is confirmed by the fact that the rail workshops are lined with replacement bogies with new wheels fitted. Apart from producing a more efficient and less polluting locomotive, it is also the intention to reduce maintenance costs. Slip slide control with predictive wheel diameter would have avoided this situation. The aim is to extend the servicing of locomotive bogies to 10 years with this proposed system instead of 3 years.

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6 PRINCIPLE OF ADHESION CONTROL

The motion equations of locomotive are governed by (1) and (2). (1) describes the motion of rolling stock of electric commuter train, and (2) describes the motion of driving wheel of

locomotive. In equation (2), μ(vs) W g r is the wheel torque corresponding to the tangential force between rail and driving wheel as shown in Fig.18.

vt – Velocity of locomotive

vd – velocity of wheel

wd – angular velocity of wheel

W – weight of locomotive

M – weight of wheel

J – total inertia moment of wheel

Fd (vt) – resistance of locomotive

g – gravity acceleration

r – radius of wheel

t – torque delivered by traction motor

6.1 TRACTIVE EFFORT

Tractive Effort is the force that a locomotive can apply to pull a load. Tractive force between the wheels and the rail depends on the slip velocity between the wheels and the rail. Tractive force increases when the slip velocity increases a little but if it becomes too large, the tractive force decreases.

Tractive Effort is defined by the equations: Tractive Effort = Weight on the Wheel Drivers X Adhesion Adhesion = Coefficient of friction X Locomotive Adhesion Variable Equation 1 describes the motion of the driving wheel of locomotive. The motion equations of locomotive are governed by (1) and (2). (1) describes the motion of rolling stock of electric commuter train (2) describes the motion of driving wheel of locomotive. In equation (2), μ(vs) W g r is the wheel torque corresponding to the tangential force between rail and driving wheel as shown in Fig.18.

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-------(1)

-------(2) In the equation, μ(vs) W g r is the wheel torque corresponding to the tangential force between rail and driving wheel as shown in Fig.18.

vt -- velocity of locomotive

vd -- velocity of wheel

ωd -- angular velocity of wheel

W -- weight of locomotive

M -- weight on wheel,

J -- total inertia moment of wheel

Fd (vt) -- resistance of locomotive

g -- gravity acceleration

r - - radius of wheel

t – torque delivered by traction motor

Figure 19 The image of motion equation

Fig. 19. Characteristics between tangential force coefficient and slip velocity (Numerical simulation condition)

6.2 The Image of Motion Equation vt -- velocity of locomotive

vd -- velocity of wheel

ωd -- angular velocity of wheel

W -- weight of locomotive

M -- weight on wheel,

J -- total inertia moment of wheel

Fd(vt) -- resistance of locomotive

g -- gravity acceleration

r -- radius of wheel

t – torque delivered by traction motor

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The tangential force coefficient μ is a function of slip velocity vs, as shown in Fig.20. The peak value of tangential velocity (Numerical simulation condition) force is determined by the condition of maximum tangential force coefficient μ(vs). When the adhesion force becomes its peak value, the adhesion force coefficient also becomes its peak value. Therefore, when du/dvs = 0 is realized, the driving torque T corresponds to the maximum adhesion force. The purpose of the adhesion control system is to search the maximum point of the adhesion which corresponds to du/dvs = 0. in practice, usually the du/dt is used to assess whether du/ds is zero, which can be easily implemented by calculating the force on wheel based on the torque delivered by traction motor and the movement equation of locomotive within a certain time period, so that the desired anti-slip re-adhesion control should keep the driving torque τ near to the maximum tangential force.

Figure 20

Figure 21

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The schematic diagram for the ac traction with auxiliary system is shown in figure 4. The present invention relates to improving track adhesion in electric propulsion of a locomotive travelling on steel rails. Vehicles on rails obtain their traction and braking forces by means of friction between the wheel surface and the rail surface. In a conventional vehicle, slip and slide occur when the forces applied to the wheel are larger than the maximum friction force between the wheel and rail surfaces. Slip occurs when forward torque is applied to the wheels. Slide occurs when a braking force in the shape of reverse torque is applied to the wheels. The present invention presents a way to predict and minimize the occurrence of slip and slide based on wheel diameter, thus improving vehicle adhesion. There is a low margin in the value at which optimum tractive effort is realised, known as optimum creep. Optimum creep depends on track surface conditions, wheel circumference and vehicle speed. The power torque signal that is applied to the propulsion system is reduced when slip or slide occur as a result of track condition and vehicle speed. In conventional systems the same torque reference signal is sent to each traction inverter, thus ignoring differences in wheel circumference. This proposed design is expected to perfect the degree of slip and slide. Differences in wheel circumference due to wear cause variations in the optimum creep value at the wheel to rail surface. When the same torque is applied to the axles, the wheels with a bigger diameter will exert less traction force. In contrast, the wheels with a smaller diameter will exert a higher traction force to the rail surface thereby increasing the occurrences of slip and slide. The System compensates for differences in wheel diameter. Differences in wheel wear in electric propulsion vehicles are significant. Wheels do not naturally wear by the same margin. Wheel wear varies considerably depending on the location of a wheel on the vehicle, direction of travel and vehicle loading. Slip and slide are more likely to occur on wheels that are worn and thus have a smaller diameter than other wheels on the vehicle due to the small margin at which optimum creep is obtained. The same applies during braking where slide aggravates wheel flats and wheel wear. Accordingly, the tractive force exerted by the wheel surface on the rail surface depends on the wheel diameter. This difference will initiate slide on the smallest diameter wheel. A 10% decrease in wheel diameter has resulted in a tractive force increase of 11.5% on that wheel. The angular velocity of a wheel is directly related to the circumference of that particular wheel. Wheel diameter varies considerably due to wear with age and location within the bogie. An object of the present invention is to provide a traction control system that improves the adhesion characteristics of electric locomotives by accurately measuring differences in angular velocity of individual axles. This will determine wheel circumference and incorporating the parameters thus obtained in the traction control loop, thus decreasing the traction force in axle assemblies that have smaller wheels by a fraction that is equivalent to the difference in tractive force. The torque power generating means consists of a master controller that receives the angular velocity of each driven axle, controlling a plurality of traction inverter circuits that drive a plurality electric motors applying torque to the axles. In a first embodiment, each axle assembly consists typically of an axle, two wheels, an Alternating Current electric traction motor mounted with a direct coupled resolver to provide feedback to the Master Controller and a traction inverter coupled to the Master Controller. The vehicle typically includes a plurality of such axle assemblies, one to each axle, as well as a primary energy source, a means for controlling the primary energy source and energy conversion means such as an alternator.

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A master control circuit receives input from a plurality of resolver devices to determine the angular velocity of each axle. Angular velocity is directly related to the circumference of wheels that are mounted on each axle. The master control circuit compares the angular velocity of each axle and adjusts the traction inverter output on the axle assembly to compensate for wheel wear, resulting in the same torque at the wheel to rail surface for all wheels on the vehicle. Most buyers of locomotives still choose DC traction worldwide because they are more familiar with the operation even though it has poor efficiency. Locomotives using DC traction are inefficient because they are powered by a diesel engine and create significant carbon emission. One ac traction locomotive with a Hydrogen Fuel Cell system can replace DC locomotives and the green house emission is reduced to zero compared with both DC and conventional AC traction. It is the intention to produce a more efficient ac locomotive by predicting the required torque for an existing wheel diameter so that adhesion can be maintained throughout the useful life of traction wheels. There is a definite need for hybrid ac traction on locomotives. The purpose of the project is to use Direct torque traction inverters for locomotives using the system of "Slip /slide with wheel diameter compensation". A major problem that any rail traction system has is slip during traction and slide during braking particularly when the 6 axle wheels are worn to different sizes. Bernard Schaffler designed and patented their slip / slide system with wheel diameter compensation.

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Comparison Property DTC FOC

Dynamic response to torque Very fast Fast

Coordinates reference frame alpha, beta (stator) d, q (rotor)

Low speed (< 5% of nominal) behaviour

Requires speed sensor

for continuous braking

Good with position or speed sensor

Controlled variables torque & stator flux rotor flux, torque current iq & rotor flux current id vector components

Steady-state torque/current/flux ripple & distortion

Low (requires high quality

current sensors)

Low

Parameter sensitivity, sensor less

Stator resistance d, q inductances, rotor resistance

Parameter sensitivity, closed-loop

d, q inductances, flux

(near zero speed only)

d, q inductances, rotor resistance

Rotor position measurement Not required Required (either sensor or estimation)

Current control Not required Required

PWM modulator Not required Required

Coordinate transformations Not required Required

Switching frequency

Varies widely around

average frequency

Constant

Switching losses

Lower (requires high

quality current sensors)

Low

Audible noise spread spectrum sizzling noise constant frequency whistling noise

Control tuning loops speed (PID control) speed (PID control), rotor flux control (PI), id and iq current controls (PI)

Complexity/processing requirements

Lower Higher

Typical control cycle time 10-30 microseconds 100-500 microseconds

The direct torque method performs very well even without speed sensors. However, the flux estimation is usually based on the integration of the motor phase voltages. Due to the inevitable errors in the voltage measurement and stator resistance estimate the integrals tend to become erroneous at low speed. Therefore, it is not possible to control the motor if the output frequency of the variable frequency drive is zero.

However, by careful design of the control system it is possible to have the minimum frequency in the range 0.5 Hz to 1 Hz that is enough to make possible to start an induction motor with full torque from a standstill situation. A reversal of the rotation direction is also possible if the speed is passing through the zero range rapidly enough to prevent excessive flux estimate deviation.

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If continuous operation at low speeds including zero frequency operation is required, a speed or position sensor can be added to the DTC system. With the sensor, high accuracy of the torque and speed control can be maintained in the whole speed range.

7 REDUCED CARBON EMISSION USING AC TRACTION

The planned outcome of this project is to design and produce subsystems in particular traction and auxiliary power systems using hydrogen fuel hybrid locomotive. This will provide significant reduction in greenhouse gases presently emitted from diesel locomotives. This illusion is rapidly destroying the utility networks throughout the world. The key features of the proposed subsystems will be:

• greater efficiency than existing ac system

• reduction of the carbon footprint compared to diesel locomotives

• use of innovative design and modern technology

• unique design at the forefront of technology in the rail industry

• provide comparable or enhanced performance to existing systems

• improve fuel consumption

• save maintenance costs,

• increase opportunities to refurbish, upgrade and re use exiting locomotives avoiding

the unnecessary cost of importing or building new locomotives.

The commercialisation of this project will be for new electric locomotives or retrofitting to existing DC locomotives. This can apply to both new and old locomotives. The technology is attractive to overseas rail companies, significant opportunities will be created for export markets. The planned project outcome is an innovative product called Transpower Locomotive System. It is a master control system that controls the ac traction motors on a locomotive. It will prove that traction on hybrid locomotive with ac traction is far more efficient than that of DC locomotives. Slip/slide control with wheel diameter compensation on a Schaffler Consulting Locomotive System will reduce wheel wear and maintenance costs. The system will provide a more fuel-efficient AC traction locomotive which leads to a significant reduction in greenhouse gas emission.

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The project includes the use of:

1. A traction system to maintain equal wheel adhesion, improve traction hence efficiency resulting in fuel and maintenance saving, and

2. Regenerated power from the traction system to provide power to charge batteries and provide power for auxiliaries on the locomotive.

3. To assist calculations, the following constants have been assumed and utilised until such time as a particular locomotive becomes available.

8 General Information about existing Traction Motors

Traction motor poles 4

Traction motor Cos φ 0.78

Traction motor

Efficiency

0.93

Mass of

locomotive(tonne)

132

Gear ratio 61:16

Wheel diameter(mm) 1016 (new)

Wheel diameter(mm) 985 (half worn)

Wheel diameter(mm) 916 (full worn)

Gear Efficiency 98 %

Overall locomotive

efficiency

86%

8.1 Existing Diesel Locomotive System It must be understood that the wheels of a locomotive are fixed in pairs through a rigid axle.

A four-axle locomotive is called a BO_BO (8 wheels) A six-axle locomotive is called a CO_CO (12 wheels)

An eight-axle locomotive is called a DO_DO (16 wheels). {Used in Brazil}

Auxiliary System Auxiliary Inverter System • Compressors

• Air particle filtration

• Traction motor blowers

• Radiator fan blowers

• Traction inverter water pump

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Traction System • Traction Inverters

• Slip control

• Brake Inverters

• Slide control

Battery Powered Auxiliary System

• Battery charger

• SMPS 24 Vdc

• Head light converter

• Cabinverter for driver

• Air conditioner

The author’s Locomotive research includes two major sub-systems and more branch systems.

8.2 MAJOR SUB-SYSTEM- Auxiliary System In an ac traction diesel locomotive, the auxiliary alternator will be eliminated. Existing DC and ac traction locomotives use an auxiliary alternator driven by a diesel engine to provide power for loads such as the battery charger, brake compressors, radiator fans, traction motor blowers, air conditioning, dynamic brake blowers, auxiliary cabinverter for headlights and computer power. Instead, with the Transpower System, power for the auxiliary system is drawn from the traction batteries or from regenerative power during braking or coasting. The weight of both traction and auxiliary equipment on the locomotive is reduced so that more hydrogen fuel can be carried instead of dead loads.

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8.3 MAJOR SUB-SYSTEM – TRACTION The Traction System is a high frequency fast responding system. It will measure wheel diameter of each individual wheel and detect the point of slip and slide of the wheel by comparing the wheel speed against the master axle speed. Accurate torque measurement and the sensitive control of torque to each individual traction motor are based on the circumferential torque for each individual axle. There will be a traction motor assigned to each axle. By preventing slip in traction and slide in braking, the traction system maintains constant adhesion over the life of a set of wheels to the rails. It reduces the wear and tear of both the wheels and the rails. It is expected that wheel changing will extend to at least 8 years or more instead of 3 years. In the Transpower Locomotive System, tractive effort is increased so it is possible for the locomotive to haul a greater load on a continuous basis because wheel wear is always taken into account. The two major sub-systems are not independent to each other.

9 LOCOMOTIVE VIGILANCE CONTROL Vigilance Control will need to be part of the designed. Vigilance includes:

• Human interface – driver control and human feedback • Notch control for multiple locomotives coupled on to one train • System automatic starting and speed control. • For hybrid system, control of battery charge level combined.

This application covers the innovation and prototype building of the Schaffler Locomotive System and intensive testing of the system with outsourced traction motors. Once this has been achieved, the system and the traction motor can be fitted to either an existing locomotive or a newly built locomotive. The project is committed to high efficiency power electronic products, research and development. Development will eliminate the need for a large traction diesel engine and alternator which reduces the excessive weight on the locomotive. Weight reduction will depend on the individual locomotive being upgraded and can expect reductions of up to 70% in weight. Apart from locomotives existing rolling stock are Diesel Multiple Units (DMU), electric trains (EMUs) and maintenance locomotives for underground railways. The proposed development relates to improving track adhesion in electric propulsion of a locomotive travelling on steel rails. Vehicles on rails obtain their traction and braking forces by means of friction between the wheel surface and the rail surface. In a conventional vehicle, slip and slide occur when the forces applied to the wheel are larger than the maximum friction force between the wheel and rail surfaces. Slip occurs when forward torque is applied to the wheels. Slide occurs when a braking force in the shape of reverse torque is applied to the wheels. The present development presents a way to predict and minimize the occurrence of slip and slide based on wheel diameter, thus improving vehicle adhesion.

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Maximum tractive effort is obtained when each powered axle of the vehicle is rotating at such an angular velocity that its actual peripheral speed is marginally higher than the actual speed of the vehicle. The difference between the actual velocity of the vehicle and the wheel speed is generally referred to in literature as creep. There is a low margin in the value at which optimum tractive effort is realised, known as optimum creep. Optimum creep depends on track surface conditions, wheel circumference and vehicle speed. The power torque signal that is applied to the propulsion system will be reduced when slip or slide occur as a result of track condition and vehicle speed. In conventional systems the same torque reference signal is sent to each traction inverter, thus ignoring differences in wheel circumference. Differences in wheel circumference due to wear cause variations in the optimum creep value at the wheel to rail surface. When the same torque is applied to the axles, the wheels with a bigger diameter will exert less traction force. In contrast, the wheels with a smaller diameter will exert a higher traction force to the rail surface thereby increasing the occurrences of slip and slide. The Transpower System will compensate for differences in wheel diameter. Differences in wheel wear in existing locomotive propulsion vehicles are significant. Not all wheels wear by the same margin. Wheel wear varies considerably depending on the location of a wheel on the vehicle, direction of travel and vehicle loading. Slip and slide are more likely to occur on wheels that are worn and thus have a smaller diameter than other wheels on the vehicle due to the small margin at which optimum creep is obtained. The same applies during braking where slide aggravates wheel flats and wheel wear. Accordingly, the tractive force exerted by the wheel surface on the rail surface depends on the wheel diameter. This difference will initiate slide on the smallest diameter wheel. A 10% decrease in wheel diameter has resulted in a tractive force increase of 11.5% on that wheel. The angular velocity of a wheel is directly related to the circumference of that particular wheel. Wheel diameter varies considerably due to wear with age and location within the bogie. An object of the present invention is to provide a traction control system that improves the adhesion characteristics of electric locomotives by accurately measuring differences in angular velocity of individual axles. This will determine wheel circumference and incorporating the parameters thus obtained in the traction control loop, thus decreasing the traction force in axle assemblies that have smaller wheels by a fraction that is equivalent to the difference in tractive force. The torque power generating means consists of a master controller that receives the angular velocity of each driven axle, controlling a plurality of traction inverter circuits that drive a plurality electric motors applying torque to the axles. In a first embodiment, each axle assembly consists typically of an axle, two wheels, an Alternating Current electric traction motor mounted with a direct coupled resolver to provide feedback to the Master Controller and a traction inverter coupled to the Master Controller. The vehicle typically includes a plurality of such axle assemblies, one to each axle, as well as a primary energy source, and a means for controlling the primary energy source.

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10 PRINCIPLE AND COMPARISON The competitive advantage is the ability to maintain adhesion of the traction wheels and prevent wheel wear.

Schaffler Consulting principle is PREDICTIVE.

The GE system is RESPONSIVE. By predicting wheel diameter, we will prevent slip or slide and therefore provide an improved adhesion so that a larger load can be hauled by each locomotive and reduce wheel wear.

Transparent picture of DO-DO Hydrogen Fuel Cell Locomotive

Transparent picture of CO_CO diesel locomotive

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11 Typical Specification and Technical Information

about a typical 132t AC traction diesel locomotive. To assist calculations, the following constants have been assumed and utilised:

Traction motor poles 4

Traction motor Cos φ 0.78

Traction motor Efficiency 0.93

Mass of locomotive(tonne) 132

Gear ratio 61:16

Wheel diameter(mm) 1016 (new)

Wheel diameter(mm) 985 (half worn)

Wheel diameter(mm) 916(full worn)

Gear Efficiency 98 %

Overall locomotive efficiency

86%

132 t C0 - C0 locomotive Engine: MTU 20V 4000 R43L

Engine idle speed: 600 r/min

Engine full speed: 1800 r/min

Engine power rating: 3,000 kW

Auxiliary power rating: 180 kW

Continuous service speed: 21 km/h

Starting tractive effort: 518 kN

Continuous tractive effort: 426 kN

Maximum braking effort: 258 kN

Standard 500 kW Traction Motor Rated power: 500 kW

Poles: 4

Rated voltage: 690 V

Rated current: 580 A

Rated torque: 11,422 N·m

Rated speed: 418 r/min

Maximum speed at nominal power: 2,850 r/min

Maximum speed: 3,160 r/min

Starting torque: 11,738 N·m

Maximum voltage: 780 V

Ventilation: Forced Air

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12 Locomotive wheel data table All dimensions in mm

Wheel type W61, W63, W64

New wheel diameter (mm) 1016

New wheel circumference (mm) 3193

Condemn wheel diameter (mm) 930

Thickness of Rim at Condemn on Back Flange (mm) 38

Thickness of Tread at Condemn on Back Flange (mm) 6

Minimum flange width (mm) 19

Maximum flange height (mm) 35

Maximum tread hollowing (mm) 3

Wheel width (mm) 130

Wheel drawing W61 – 206-328/1 W63 – 206-328/3 W64 – 206-328/4

Clearance to structure gauge (mm) 40 Table 2

Circumference of new wheel 3191.8 mm

Circumference of worn wheel 2921.6 mm

13 Tractive & braking effort diagram The comparison below is between the conventional diesel locomotive with all auxiliary alternators coupled to the main alternator and the locomotive with the proposed system. The table below shows the comparison between an existing ac traction locomotive and locomotive loaded with proposed locomotive System.

Figure 22

-300

-200

-100

0

100

200

300

400

500

600

0 20 40 60 80 100 120 140

Speed [km/h]

Traction effort [kN]

Fcont [kN]

F [kN]

B [kN]

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DC Locomotive

Competitor’s ac Locomotive

ac Locomotive with proposed locomotive System

Loading (trailing tons 1:50 grade @ 19 kph

1,396 1,904 2,224

Life (Years) 25 25 25

Usage (km/year) 200,000 200,000 200,000

Freight ton km 6,980,000,000 9,520,000,000 11,120,000,000

Initial Capital Cost 3,775,000 $5,500,000 $5,500,000

Maintenance Costs

Routine maintenance $3,070,000 $3,070,000 $3,070,000

Major maintenance $2,213,000 $1,963,000 $1,963,000

Bogie change out with new wheels

400,000 400,000 200,000

Fuel cost $67,650,282 $47,412,540 $40,639,320

Total Cost $76,708,282 $58,345,540 $51,372,320

Emission (g/ftkm) 14.12 7.26 0

Emission cost $1,970,460 $1,383,060 0

Emission cost / FTkm 0.0282 0.0145 0

Total cost (including carbon trading)

$78,678,742 $59,728,600 $51,372,320

Total Cost per FTkm (cents) 1.13 0.63 0.54

One 132-ton locomotive will operate for 5000 hours/per year. Over the life time of 25 years, there will be 6,250,000 kW hours of power saving. Information obtained from MTU (engine builder) for their 2700 kW engine i.e. 132 ton locomotive is that 200 g/kW.h, will save 1,250,000,000 g of fuel. This represents 3,970,588,235 kg CO2 saving in 25 years using the proposed Auxiliary System.

14 LOCOMOTIVE WHOLE LIFE CONCLUSIONS The use of an auxiliary alternator means that it is not possible to use traction power generated by the locomotive during braking or when travelling downhill. The Transpower System will not use an auxiliary alternator. The power for all auxiliary loads is derived from the Hydrogen fuel cells and batteries. See the schematic for the ac traction with auxiliary system attached. Every auxiliary motor is driven by a variable frequency inverter. The auxiliary master controller determines the speed of each motor so that the locomotive runs at optimum efficiency. The radiator fans blow only enough to keep the traction motors

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temperature at 80 °C. No power is wasted. The compressor motors run at variable speed to create the correct air pressure. They reduce speed when the pressure approaches the desired pressure and turn off when it is correct. They will not just run all the time like on conventional locomotives. On the Transpower system, when the locomotives travel downhill or is braking, the traction power regenerated charges the batteries and is used by the auxiliary system. The auxiliary system will have a power saving of up to 40% for auxiliary power. The auxiliary alternator on a 132 ton locomotive is usually sized at 200 kVA. It is common to draw an average load of 165 kW. All that power comes from diesel fuel in conventional locomotives with an auxiliary alternator. However, the saving will depend on ambient temperature. This is because all the motors are controlled by variable frequency inverters which will run at a speed to suit the demand dependant on temperature. On average, the power saving will be 30% at 20° ambient temperature. On the 132ton locomotive, the auxiliaries require of 165 kW of power, which means there are nearly 50 kW saving.

Comparison Property DTC FOC

Dynamic response to torque

Very fast Fast

Coordinates reference frame alpha, beta (stator) d, q (rotor)

Low speed (< 5% of nominal) behaviour

Requires speed sensor for continuous braking

Good with position or speed sensor

Controlled variables torque & stator flux

rotor flux, torque current iq & rotor flux current id vector components

Steady-state torque/current/flux ripple & distortion

Low (requires high quality current sensors)

Low

Parameter sensitivity, sensor less Stator resistance d, q inductances, rotor resistance

Parameter sensitivity, closed-loop d, q inductances, flux (near zero speed only)

d, q inductances, rotor resistance

Rotor position measurement Not required Required (either sensor or estimation)

Current control Not required Required

PWM modulator Not required Required

Coordinate transformations Not required Required

Switching frequency Varies widely around average frequency

Constant

Switching losses Lower (requires high quality current sensors)

Low

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Audible noise spread spectrum sizzling noise

constant frequency whistling noise

Control tuning loops speed (PID control)

speed (PID control), rotor flux control (PI), id and iq current controls (PI)

Complexity/processing requirements

Lower Higher

Typical control cycle time 10-30 microseconds 100-500 microseconds

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15 References The patent 8645011 was written and designed by Bernard Schaffler. Wheel Slip Control based on traction force estimation of electric locomotives. Gerald Ledwich. New reliable start up DTC technique for induction motor drive. Gerald Ledwich. Rolling stock references where Schaffler Pty Ltd were the suppliers for intelligent battery chargers. Wood Mackenzie predicts about grey hydrogen that will remain the cheapest type through to 2040. Assistance from Bollard in Canada related to fuel cells. DCT reference provided by ABB Figures for electrification of tracks in various counties. Reference University of British Columbia. Hydrogen Storage for renewable Energy Systems by Even Grey of Griffith University.

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