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Aero Dynamic Wind Mill with Reverse Charge Protection
AERO DYNAMIC WIND MIL WITH REVERSE CHARGE
PROTECTION
1.1 BLOCK DIAGRAM
Fig: 1.1 Block Diagram
1
AT89S52
Power
Supply
Unit
16X2 LCD
AC ripple
neutralizer
Unidirectio
nal Current
Controller
Rechargea
ble Battery Inverter
Voltage
SamplerADC
Contras
tAero
dynamic
wind blade
arrangemen
t
Geared DC
motor
ON/ OFF
control
switch
AC 230V
Load
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2. EMBEDDED SYSTEMS
An embedded system is a system which is going to do a predefined specified task is theembedded system and is even defined as combination of both software and hardware. A general-
purpose definition of embedded systems is that they are devices used to control, monitor or assist
the operation of equipment, machinery or plant. "Embedded" reflects the fact that they are an
integral part of the system. At the other extreme a general-purpose computer may be used to control
the operation of a large complex processing plant, and its presence will be obvious.
All embedded systems are including computers or microprocessors. Some of these
computers are however very simple systems as compared with a personal computer.
The very simplest embedded systems are capable of performing only a single function or set
of functions to meet a single predetermined purpose. In more complex systems an application
program that enables the embedded system to be used for a particular purpose in a specific
application determines the functioning of the embedded system. The ability to have programs means
that the same embedded system can be used for a variety of different purposes. In some cases a
microprocessor may be designed in such a way that application software for a particular purpose can
be added to the basic software in a second process, after which it is not possible to make further
changes. The applications software on such processors is sometimes referred to as firmware.
The simplest devices consist of a single microprocessor (often called a "chip), which may itself be
packaged with other chips in a hybrid system or Application Specific Integrated Circuit (ASIC). Its input
comes from a detector or sensor and its output goes to a switch or activator which (for example) may start or
stop the operation of a machine or, by operating a valve, may control the flow of fuel to an engine.
As the embedded system is the combination of both software and hardware
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Figure: 2 Block diagram of Embedded System
Software deals with the languages like ALP, C, and VB etc., and Hardware deals with Processors,
Peripherals, and Memory.
Memory: It is used to store data or address.
Peripherals: These are the external devices connected
Processor: It is an IC which is used to perform some task
Applications of embedded systems
Manufacturing and process control
Construction industry
Transport
Buildings and premises
Domestic service
Communications
Office systems and mobile equipment
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Embedded
System
Software Hardware
ALP
C
VB
Etc.,
Processor
Peripherals
memory
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Banking, finance and commercial
Medical diagnostics, monitoring and life support
Testing, monitoring and diagnostic systems
Processors are classified into four types like:
Micro Processor (p)
Micro controller (c)
Digital Signal Processor (DSP)
Application Specific Integrated Circuits (ASIC)
Micro Processor (p):
A siliconchipthat contains a CPU. In the world ofpersonal computers, the terms microprocessorand CPU are used interchangeably. At the heart of all personal computers and most workstations
sits a microprocessor. Microprocessors also control the logic of almost all digital devices, from
clock radios to fuel-injection systemsfor automobiles.
Three basic characteristics differentiate microprocessors:
Instruction set: The set of instructions that the microprocessor can execute.
Bandwidth : The number ofbits processed in a single instruction.
Clock speed : Given in megahertz (MHz), the clock speed determines how many instructions per
second theprocessorcan execute.
In both cases, the higher the value, the more powerful the CPU. For example, a 32-bit
microprocessor that runs at 50MHz is more powerful than a 16-bit microprocessor that runs at
25MHz. In addition to bandwidth and clock speed, microprocessors are classified as being either
RISC (reduced instruction set computer) orCISC (complex instruction set computer).
A microprocessor has three basic elements, as shown above. The ALU performs allarithmetic computations, such as addition, subtraction and logic operations (AND, OR, etc). It is
controlled by the Control Unit and receives its data from the Register Array. The Register Array is
a set of registers used for storing data. These registers can be accessed by the ALU very quickly.
Some registers have specific functions - we will deal with these later. The Control Unit controls
the entire process. It provides the timing and a control signal for getting data into and out of the4
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registers and the ALU and it synchronizes the execution of instructions (we will deal with
instruction execution at a later date).
Micro Controller (c):
A microcontroller is a small computer on a single integrated circuit containing a processor
core, memory, and programmable input/output peripherals. Program memory in the form ofNOR
flash orOTP ROM is also often included on chip, as well as a typically small amount of RAM.
Microcontrollers are designed for embedded applications, in contrast to the microprocessors used
in personal computers or other general purpose applications.
Figure: 2 Block Diagram of Micro Controller (c)
Digital Signal Processors (DSPs):
Digital Signal Processors is one which performs scientific and mathematical operation.
Digital Signal Processor chips - specialized microprocessors with architectures designed specifically
for the types of operations required in digital signal processing. Like a general-purpose
microprocessor, a DSP is a programmable device, with its own native instruction code. DSP chips
are capable of carrying out millions of floating point operations per second, and like their better-
known general-purpose cousins, faster and more powerful versions are continually being
introduced. DSPs can also be embedded within complex "system-on-chip" devices, often containing
both analog and digital circuitry.
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Timer, Counter,
serial
communication
ROM, ADC, DAC,
Timers, USART,
Oscillators
Etc.,
ALU
CU
Memor
y
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Application Specific Integrated Circuit (ASIC):
ASIC is a combination of digital and analog circuits packed into an IC to achieve the desired
control/computation function
ASIC typically contains
CPU cores for computation and control
Peripherals to control timing critical functions
Memories to store data and program
Analog circuits to provide clocks and interface to the real world which is analog in nature
I/Os to connect to external components like LEDs, memories, monitors etc.
Computer Instruction Set
There are two different types of computer instruction set there are:
1. RISC (Reduced Instruction Set Computer) and
2. CISC (Complex Instruction Set computer)
Reduced Instruction Set Computer (RISC)
A RISC (reduced instruction set computer) is a microprocessor that is designed to perform a
smaller number of types of computer instruction so that it can operate at a higher speed (perform
more million instructions per second, or millions of instructions per second). Since each instruction
type that a computer must perform requires additional transistors and circuitry, a larger list or set of
computer instructions tends to make the microprocessor more complicated and slower in operation.
Besides performance improvement, some advantages of RISC and related design improvements are:
A new microprocessor can be developed and tested more quickly if one of its aims is to be less
complicated.
Operating system and application programmers who use the microprocessor's instructions will find
it easier to develop code with a smaller instruction set.
The simplicity of RISC allows more freedom to choose how to use the space on a microprocessor.
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Higher-level language compilers produce more efficient code than formerly because they have
always tended to use the smaller set of instructions to be found in a RISC computer.
RISC characteristics:
Simple instruction set:
In a RISC machine, the instruction set contains simple, basic instructions, from which more
complex instructions can be composed.
Same length instructions.
Each instruction is the same length, so that it may be fetched in a single operation.
1 machine-cycle instructions.
Most instructions complete in one machine cycle, which allows the processor to handle several
instructions at the same time. This pipelining is a key technique used to speed up RISC machines.
Complex Instruction Set Computer (CISC)
CISC, which stands for Complex Instruction Set Computer, is a philosophy for designing
chips that are easy to program and which make efficient use of memory. Each instruction in a CISC
instruction set might perform a series of operations inside the processor. This reduces the number of
instructions required to implement a given program, and allows the programmer to learn a small but
flexible set of instructions.
The advantages of CISC
At the time of their initial development, CISC machines used available technologies to
optimize computer performance.
Microprogramming is as easy as assembly language to implement, and much less expensive than
hardwiring a control unit.
The ease of micro-coding new instructions allowed designers to make CISC machines upwardly
compatible: a new computer could run the same programs as earlier computers because the new
computer would contain a superset of the instructions of the earlier computers.
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As each instruction became more capable, fewer instructions could be used to implement a given
task. This made more efficient use of the relatively slow main memory.
Because micro program instruction sets can be written to match the constructs of high-level
languages, the compiler does not have to be as complicated.
The disadvantages of CISC:
Still, designers soon realized that the CISC philosophy had its own problems, including:
Earlier generations of a processor family generally were contained as a subset in every new version
--- so instruction set & chip hardware become more complex with each generation of computers.
So that as many instructions as possible could be stored in memory with the least possible wasted
space, individual instructions could be of almost any length---this means that different instructions
will take different amounts of clock time to execute, slowing down the overall performance of the
machine.
Many specialized instructions aren't used frequently enough to justify their existence ---
approximately 20% of the available instructions are used in a typical program.
CISC instructions typically set the condition codes as a side effect of the instruction. Not only does
setting the condition codes take time, but programmers have to remember to examine the condition
code bits before a subsequent instruction changes them.
Memory Architecture
There two different types memory architectures there are:
Harvard Architecture
Von-Neumann Architecture
Harvard Architecture
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Computers have separate memory areas for program instructions and data. There are two or
more internal data buses, which allow simultaneous access to both instructions and data. The CPU
fetches program instructions on the program memory bus.
The Harvard architecture is a computer architecture with physically separate storage andsignal pathways for instructions and data. The term originated from the Harvard Mark I relay-based
computer, which stored instructions on punched tape(24 bits wide) and data in electro-mechanical
counters. These early machines had limited data storage, entirely contained within the central
processing unit, and provided no access to the instruction storage as data. Programs needed to be
loaded by an operator, the processor could notbootitself.
Figure: 2 Harvard Architecture
Modern uses of the Harvard architecture
The principal advantage of the pure Harvard architecture - simultaneous access to more than
one memory system - has been reduced by modified Harvard processors using modern CPU cache
systems. Relatively pure Harvard architecture machines are used mostly in applications where
tradeoffs, such as the cost and power savings from omitting caches, outweigh the programming
penalties from having distinct code and data address spaces.
Digital signal processors (DSPs) generally execute small, highly-optimized audio or video
processing algorithms. They avoid caches because their behavior must be extremely reproducible.
The difficulties of coping with multiple address spaces are of secondary concern to speed of
execution. As a result, some DSPs have multiple data memories in distinct address spaces to
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facilitate SIMD and VLIW processing. Texas Instruments TMS320 C55x processors, as one
example, have multiple parallel data busses (two write, three read) and one instruction bus.
Microcontrollers are characterized by having small amounts of program (flash memory) and data
(SRAM) memory, with no cache, and take advantage of the Harvard architecture to speed
processing by concurrent instruction and data access. The separate storage means the program and
data memories can have different bit depths, for example using 16-bit wide instructions and 8-bit
wide data. They also mean that instruction pre-fetch can be performed in parallel with other
activities. Examples include, the AVRby Atmel Corp, the PIC by Microchip Technology, Inc. and
the ARM Cortex-M3 processor (not all ARM chips have Harvard architecture).
Von-Neumann Architecture
A computer has a single, common memory space in which both program instructions and
data are stored. There is a single internal data bus that fetches both instructions and data. They
cannot be performed at the same time
The Von Neumann architecture is a design model for a stored-program digital computer
that uses a central processing unit (CPU) and a single separate storage structure ("memory") to hold
both instructions and data. It is named after the mathematician and early computer scientist John
von Neumann. Such computers implement a universal Turing machine and have a sequential
architecture.
A stored-programdigital computeris one that keeps its programmed instructions, as well
as its data, in read-write, random-access memory (RAM). Stored-program computers were
advancement over the program-controlled computers of the 1940s, such as the Colossus and the
ENIAC, which were programmed by setting switches and inserting patch leads to route data and to
control signals between various functional units. In the vast majority of modern computers, the
same memory is used for both data and program instructions. The mechanisms for transferring the
data and instructions between the CPU and memory are, however, considerably more complex thanthe original von Neumann architecture.
The terms "von Neumann architecture" and "stored-program computer" are generally used
interchangeably, and that usage is followed in this article.
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Figure: 2 Schematic of the Von-Neumann Architecture.
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Basic Difference between Harvard and Von-Neumann Architecture
The primary difference between Harvard architecture and the Von Neumann architecture is in the
Von Neumann architecture data and programs are stored in the same memory and managed by the
same information handling system.
Whereas the Harvard architecture stores data and programs in separate memory devices and they are
handled by different subsystems.
In a computer using the Von-Neumann architecture without cache; the central processing unit
(CPU) can either be reading and instruction or writing/reading data to/from the memory. Both of
these operations cannot occur simultaneously as the data and instructions use the same system bus.
In a computer using the Harvard architecture the CPU can both read an instruction and access data
memory at the same time without cache. This means that a computer with Harvard architecture can
potentially be faster for a given circuit complexity because data access and instruction fetches do
not contend for use of a single memory pathway.
Today, the vast majority of computers are designed and built using the Von Neumann architecture
template primarily because of the dynamic capabilities and efficiencies gained in designing,
implementing, operating one memory system as opposed to two. Von Neumann architecture may be
somewhat slower than the contrasting Harvard Architecture for certain specific tasks, but it is much
more flexible and allows for many concepts unavailable to Harvard architecture such as self
programming, word processing and so on.
Harvard architectures are typically only used in either specialized systems or for very specific uses.It is used in specialized digital signal processing (DSP), typically for video and audio processing
products. It is also used in many small microcontrollers used in electronics applications such as
Advanced RISK Machine (ARM) based products for many vendors.
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3. BLOCK DESCRIPTION
3.1 POWER SUPPLY:
The input to the circuit is applied from the regulated power supply. The a.c. input i.e., 230V fromthe mains supply is step down by the transformer to 12V and is fed to a rectifier. The output
obtained from the rectifier is a pulsating d.c voltage. So in order to get a pure d.c voltage, the output
voltage from the rectifier is fed to a filter to remove any a.c components present even after
rectification. Now, this voltage is given to a voltage regulator to obtain a pure constant dc voltage.
Fig 3.1: Power supply
Transformer:
13
RegulatorFILTER
HBridge
Rectifier
Step down
transformer
230V AC
50Hz D.COutput
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Usually, DC voltages are required to operate various electronic equipment and these
voltages are 5V, 9V or 12V. But these voltages cannot be obtained directly. Thus the a.c input
available at the mains supply i.e., 230V is to be brought down to the required voltage level. This is
done by a transformer. Thus, a step down transformer is employed to decrease the voltage to a
required level.
Fig 3.1: Transformer
Rectifier:
The output from the transformer is fed to the rectifier. It converts A.C. into pulsating D.C.
The rectifier may be a half wave or a full wave rectifier. In this project, a bridge rectifier is used
because of its merits like good stability and full wave rectification.
Fig 3.1: Rectifier
The Bridge rectifier is a circuit, which converts an ac voltage to dc voltage using both half
cycles of the input ac voltage. The Bridge rectifier circuit is shown in the figure. The circuit has four
diodes connected to form a bridge. The ac input voltage is applied to the diagonally opposite ends of
the bridge. The load resistance is connected between the other two ends of the bridge.
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For the positive half cycle of the input ac voltage, diodes D1 and D3 conduct, whereas
diodes D2 and D4 remain in the OFF state. The conducting diodes will be in series with the load
resistance RL and hence the load current flows through RL.
For the negative half cycle of the input ac voltage, diodes D2 and D4 conduct whereas, D1
and D3 remain OFF. The conducting diodes D2 and D4 will be in series with the load resistance
RL and hence the current flows through RL in the same direction as in the previous half cycle. Thus a
bi-directional wave is converted into a unidirectional wave.
Fig: 3.1 Bridge rectifier
Filter:
Capacitive filter is used in this project. It removes the ripples from the output of rectifier and
smoothens the D.C. Output received from this filter is constant until the mains voltage and load is
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maintained constant. However, if either of the two is varied, D.C. voltage received at this point
changes. Therefore a regulator is applied at the output stage .
Fig: 3.1 Capacitor Filter
Voltage regulator:
As the name itself implies, it regulates the input applied to it. A voltage regulator is an
electrical regulator designed to automatically maintain a constant voltage level. In this project,
power supply of 5V and 12V are required. In order to obtain these voltage levels, 7805 and 7812
voltage regulators are to be used. The first number 78 represents positive supply and the numbers
05, 12 represent the required output voltage levels. The L78xx series of three-terminal positive
regulators is available in TO-220, TO-220FP, TO-3, D2PAK and DPAK packages and several fixedoutput voltages, making it useful in a wide range of applications. These regulators can provide local
on-card regulation, eliminating the distribution problems associated with single point regulation.
Each type employs internal current limiting, thermal shut-down and safe area protection, making it
essentially indestructible. If adequate heat sinking is provided, they can deliver over 1 A output
current. Although designed primarily as fixed voltage regulators, these devices can be used with
external components to obtain adjustable voltage and currents.
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Fig: 3.1 voltage regulator
3.2 AERO DYNAMIC WIND BLADE
Wind turbine blades are shaped to generate the maximum power from the wind at the
minimum cost. Primarily the design is driven by the aerodynamic requirements, but economics
mean that the blade shape is a compromise to keep the cost of construction reasonable. In
particular, the blade tends to be thicker than the aerodynamic optimum close to the root, where the
stresses due to bending are greatest. The blade design process starts with a best guess compromisebetween aerodynamic and structural efficiency. The choice of materials and manufacturing process
will also have an influence on how thin (hence aerodynamically ideal) the blade can be built. For
instance, prepreg carbon fibre is stiffer and stronger than infused glass fibre. The chosen
aerodynamic shape gives rise to loads, which are fed into the structural design. Problems identified
at this stage can then be used to modify the shape if necessary and recalculate the aerodynamic
performance.
Fig: 3.2 Aero Wind Blade
The Wind:
It might seem obvious, but an understanding of the wind is fundamental to windturbine design. The power available from the wind varies as the cube of the wind speed, so twice
the wind speed means eight times the power. This is why sites have to be selected carefully: below
about 5m/s (0mph) wind speed there is not sufficient power in the wind to be useful. Conversely,
strong gusts provide extremely high levels of power, but it is not economically viable to build
machines to be able to make the most of the power peaks as their capacity would be wasted most of17
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the time. So the ideal is a site with steady winds and a machine that is able to make the most of the
lighter winds whilst surviving the strongest gusts.
As well as varying day-to-day, the wind varies every second due to turbulence caused
by land features, thermals and weather. It also blows more strongly higher above the ground thancloser to it, due to surface friction. All these effects lead to varying loads on the blades of a turbine
as they rotate, and mean that the aerodynamic and structural design needs to cope with conditions
that are rarely optimal. By extracting power, the turbine itself has an effect on the wind: downwind
of the turbine the air moves more slowly than upwind.
The wind starts to slow down even before it reaches the blades, reducing the wind
speed through the disc (the imaginary circle formed by the blade tips, also called the swept area)
and hence reducing the available power. Some of the wind that was heading for the disc divertsaround the slower-moving air and misses the blades entirely. So there is an optimum amount of
power to extract from a given disc diameter: try to take too much and the wind will slow down too
much, reducing the available power. In fact the ideal is to reduce the wind speed by about two
thirds downwind of the turbine, though even then the wind just before the turbine will have lost
about a third of its speed. This allows a theoretical maximum of 59% of the winds power to be
captured (this is called Betzs limit). In practice only 40-50% is achieved by current designs.
Number of blades:
The limitation on the available power in the wind means that the more blades there are
the less power each can extract. A consequence of this is that each blade must also be narrower to
maintain aerodynamic efficiency. The total blade area as a fraction of the total swept disc area is
called the solidity, and aerodynamically there is an optimum solidity for a given tip speed; the
higher the number of blades, the narrower each one must be. In practice the optimum solidity is low
(only a few percent) which means that even with only three blades, each one must be very narrow.
To slip through the air easily the blades must be thin relative to their width, so the limited solidity
also limits the thickness of the blades. Furthermore, it becomes difficult to build the blades strong
enough if they are too thin or the cost per blade increases significantly as more expensive materials
are required. For this reason, most large machines do not have more than three blades. The other
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factor influencing the number of blades is aesthetics: it is generally accepted that three-bladed
turbines are less visually disturbing than one- or two-bladed designs.
How blades capture wind power:
Just like an aeroplane wing, wind turbine blades work by generating lift due to their
shape. The more curved side generates low air pressures while high pressure air pushes on the other
side of the aerofoil. The net result is a lift force perpendicular to the direction of flow of the air.
The lift force increases as the blade is turned to present itself at a greater angle to the
wind. This is called the angle of attack. At very large angles of attack the blade stalls and the lift
decreases again. So there is an optimum angle of attack to generate the maximum l if .Lift & drag
vectors. There is, unfortunately, also a retarding force on the blade: the drag. This is the force
parallel to the wind flow, and also increases with angle of attack. If the aerofoil shape is good, the
lift force is much bigger than the drag, but at very high angles of attack, especially when the blade
stalls, the drag increases dramatically. So at an angle slightly less than the maximum lift angle, the
blade reaches its maximum lift/drag ratio. The best operating point will be between these two
angles. Since the drag is in the downwind direction, it may seem that it wouldnt matter for a wind
turbine as the drag would be parallel to the turbine axis, so wouldnt slow the rotor down. It would
just create thrust, the force that acts parallel to the turbine axis hence has no tendency to speed up
or slow down the rotor. When the rotor is stationary (e.g. just before start-up), this is indeed the
case. However the blades own movement through the air means that, as far as the blade is
concerned, the wind is blowing from a different angle. This is called apparent wind. The apparent
wind is stronger than the true wind but its angle is less it rotates the angles of the lift and drag to
reduce the effect of lift force pulling the blade round and increase the effect of drag slowing it
down. It also means that the lift force contributes to the thrust on the rotor. The result of this is that,
to maintain a good angle of attack, the blade must be turned further from the true wind angle.
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Fig: 3.2 Angle of attack of wind
Fig: 3.2 angle of wind blow
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Fig: 3.2 contact of wind on wind mill
Apparent wind angles
The closer to the tip of the blade you get, the faster the blade is moving through the air
and so the greater the apparent wind angle is. Thus the blade needs to be turned further at the tips
than at the root, in other words it must be built with a twist along its length. Typically the twist is
around 0-20 from root to tip. The requirement to twist the blade has implications on the ease of
manufacture.
Blade section shape
Apart from the twist, wind turbine blades have similar requirements to aeroplane wings,
so their cross-sections are usually based on a similar family of shapes. In general the best lift/drag
characteristics are obtained by an aerofoil that is fairly thin: its thickness might be only 0-5% of its
chord length (the length across the blade, in the direction of the wind flow).
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Blade twist:
If there were no structural requirements, this is how a wind turbine blade would be
proportioned, but of course the blade needs to support the lift, drag and gravitational forces acting
on it. These structural requirements generally mean the aerofoil needs to be thicker than the
aerodynamic optimum, especially at locations towards the root (where the blade attaches to the hub)
where the bending forces are greatest. Fortunately that is also where the apparent wind is moving
more slowly and the blade has the least leverage over the hub, so some aerodynamic inefficiency at
that point is less serious than it would be closer to the tip. Having said this, the section cant get too
thick for its chord length or the air flow will separate from the back of the blade similar to what
happens when it stalls and the drag will increase dramatically.
Fig: 3.2 Blade Twist on Wind Mill
To increase thickness near the root without creating a very short, fat, aerofoil section,
some designs use a flat back section. This is either a standard section thickened up to a square
trailing (back) edge, or a longer aerofoil shape that has been truncated. This reduces the drag
compared to a rounder section, but can generate more noise so its suitability depends on the wind
farm site. There is a trade-off to be made between aerodynamic efficiency and structural efficiency
even if a thin blade can be made strong and stiff enough by using lots of reinforcement inside, it
might still be better to make the blade a bit thicker (hence less aerodynamically efficient) if it saves
so much cost of material that the overall cost of electricity is reduced. The wind is free after all; its
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only the machine that we have to pay for. So there is inevitably some iteration in the design process
to find the optimum thickness for the blade.
Blade platform shape:
The platform shape is chosen to give the blade an approximately constant slowing effect
on the wind over the whole rotor disc (i.e. the tip slows the wind to the same degree as the centre or
root of the blade). This ensures that none of the air leaves the turbine too slowly (causing
turbulence), yet none is allowed to pass through too fast (which would represent wasted energy).
Remembering Betzs limit discussed above, this results in the maximum power extraction.
Because the tip of the blade is moving faster than the root, it passes through more volume of air,
hence must generate a greater lift force to slow that air down enough. Fortunately, lift increases
with the square of speed so its greater speed more than allows for that. In reality the blade can be
narrower close to the tip than near the root and still generate enough lift. The optimum tapering of
the blade platforms as it goes outboard can be calculated; roughly speaking the chord should be
inverse to the radius. So if the chord was 2m at 10m radius, it should be 10m at 1m radius. This
relationship breaks down close to the root and tip, where the optimum shape changes to account for
tip losses. In reality a fairly linear taper is sufficiently close to the optimum for most designs,
structurally superior and easier to build than the optimum shape.
Fig: 3.2 Plane Shape of Blade
Rotational speed:
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The speed at which the turbine rotates is a fundamental choice in the design, and is
defined in terms of the speed of the blade tips relative to the free wind speed (i.e. Before the wind
is slowed down by the turbine). This is called the tip speed ratio. High tip speed ratio means the
aerodynamic force on the blades (due to lift and drag) is almost parallel to the rotor axis, so relies on
a good lift/drag ratio. The lift/drag ratio can be affected severely by dirt or roughness on the blades.
Low tip speed ratio would seem like a better choice but unfortunately results in lower aerodynamic
efficiency, due to two effects. Because the lift force on the blades generates torque, it has an equal
but opposite effect on the wind, tending to push it around tangentially in the other direction. The
result is that the air downwind of the turbine has swirl, i.e. it spins in the opposite direction to the
blades. That swirl represents lost power so reduces the available power that can be extracted from
the wind. Lower rotational speed requires higher torque for the same power output, so lower tip
speed results in higher wake swirl losses.
Fig: 3.2 Rotational Speed
The other reduction in efficiency at low tip speed ratio comes from tip losses, where high-
pressure air from the upwind side of the blade escapes around the blade tip to the low pressure side,
thereby wasting energy. Since power = force x speed, at slower rotational speed the blades need to
generate more lift force to achieve the same power. To generate more lift for a given length the
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blade has to be wider, which means that, geometrically speaking, a greater proportion of the blades
length can be considered to be close to the tip. Thus more of the air contributes to tip losses and the
efficiency decreases. Various techniques can be used to limit tip losses such as winglets (commonly
seen on airliners) but few are employed in practice owing to their additional cost. The higher lift
force on a wider blade also translates to higher loads on the other components such as the hub and
bearings, so low tip speed ratio will increase the cost of these items. On the other hand the wide
blade is better able to carry the lift force (as discussed previously), so the blade itself may be
cheaper. All this means that turbine designers typically compromise on tip speed ratios in the
region of -0, so at design wind speed (usually 2-5 meters per second) the blade tip can be moving at
around 20 m/s (approximately 20 miles per hour). There are practical limits on the absolute tip
speed too: at these speeds, bird impacts and rain erosion start to become a problem for the longevity
of the blades and noise increases dramatically with tip speed.
Power and pitch control
For an economical design, the maximum performance of the generator and gearbox need
to be limited to an appropriate level for the turbines operating environment. The ideal situation is
for the turbine to be able to extract as much power as possible from the wind up to the rated power
of the generator, then limit the power extraction at that level as the wind increases further. Turbine
Power Curve WE Handbook- 2- Aerodynamics and Loads 9 If the blades angle is kept constant, theturbine is unable to respond to changes in wind speed. Not only does this make it impossible to
maintain an optimum angle of attack to generate the maximum power at varying wind speeds, the
only way to depower the machine in high wind speeds is by relying on the blades to stall (known
as passive stall control). This doesnt give the perfectly flat power curve above the rated wind
speed shown in the graph above, so to limit the maximum power, a passive stall-controlled turbine
will usually be operating somewhat below its maximum potential. If instead the blades are attached
via a bearing that allows the angle of attack to be varied (active pitch control), the blades can be
angled to maintain optimum efficiency right up to the design wind speed (at which the generator is
producing itsratedoutput). Above that wind speed they can be feathered, i.e. rotated in pitch to
decrease their angle of attack and hence their lift, so controlling the power. In survival conditions,
the turbine can be stopped altogether and the blades feathered to produce no turning force at all.
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An alternative to decreasing the angle of attack above the design wind speed is deliberately
to increase it to the point where the blade stalls (active stall control). This decreases lift and
increases drag, so has the desired slowing effect on blade rotation. It is also less sensitive to gusts
of wind than feathering: by decreasing the apparent wind angle, gusts increase the angle of attack so
tend to make the blade stall more. Therefore controlling blade speed by stall rather than feathering
can be beneficial in gusty conditions. Both methods are used by different designs.
3.3 DC MOTOR:
In any electric motor, operation is based on simple electromagnetism. A current-
carrying conductor generates a magnetic field; when this is then placed in an external magnetic
field, it will experience a force proportional to the current in the conductor, and to the strength of
the external magnetic field. As you are well aware of from playing with magnets as a kid, opposite
(North and South) polarities attract, while like polarities (North and North, South and South) repel.
The internal configuration of a DC motor is designed to harness the magnetic interaction between
acurrent-carrying conductor and an external magnetic field to generate rotational motion.
Fig: 3.3 DC Motor
Let's start by looking at a simple 2-pole DC electric motor (here red represents a magnet or
winding with a "North" polarization, while green represents a magnet or winding with a "South"
polarization).
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Fig:3.3 Simple 2-pole dc electric motor
Every DC motor has six basic parts -- axle, rotor (a.k.a., armature), stator, commutator,
field magnet(s), and brushes. In most common DC motors (and all that Beamers will see), the
external magnetic field is produced by high-strength permanent magnets1. The stator is the
stationary part of the motor -- this includes the motor casing, as well as two or more permanent
magnet pole pieces. The rotor (together with the axle and attached commutator) rotate with respect
to the stator. The rotor consists of windings (generally on a core), the windings being electrically
connected to the commutator. The above diagram shows a common motor layout -- with the rotor
inside the stator (field) magnets.
The geometry of the brushes, commutator contacts, and rotor windings are such that
when power is applied, the polarities of the energized winding and the stator magnet(s) are
misaligned, and the rotor will rotate until it is almost aligned with the stator's field magnets. As the
rotor reaches alignment, the brushes move to the next commutator contacts, and energize the next
winding. Given our example two-pole motor, the rotation reverses the direction ofcurrent through
the rotor winding, leading to a "flip" of the rotor's magnetic field, driving it to continue rotatin
Fig: 3.3 rotation of rotor in dc motor
In real life, though,DC motors will always have more than two poles (three is a very
common number). In particular, this avoids "dead spots" in the commutator. You can imagine how
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with our example two-pole motor, if the rotor is exactly at the middle of its rotation (perfectly
aligned with the field magnets); it will get "stuck" there. Meanwhile, with a two-pole motor, there is
a moment where the commutator shorts out the power supply (i.e., both brushes touch both
commutator contacts simultaneously). This would be bad for the power supply, waste energy, and
damage motor components as well. Yet another disadvantage of such a simple motor is that it would
exhibit a high amount oftorque "ripple" (the amount oftorqueit could produce is cyclic with the
position of the rotor).
So since most smallDCmotors are of a three-pole design, let's tinker with the workings of
one via an interactive animation (JavaScript required):
You'll notice a few things from this -- namely, one pole is fully energized at a time (but
two others are "partially" energized). As each brush transitions from one commutator contact to the
next, one coil's field will rapidly collapse, as the next coil's field will rapidly charge up (this occurs
within a few microsecond). We'll see more about the effects of this later, but in the meantime you
can see that this is a direct result of the coil windings' series wiring:
Fig: 3.3 Placing of Commutator in DC Motor
The use of an iron core armature (as in the Mabuchi, above) is quite common, and has a number of
advantages. First off, the iron core provides a strong, rigid support for the windings -- a particularly
important consideration for high-torque motors. The core also conducts heat away from the rotor
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windings, allowing the motor to be driven harder than might otherwise be the case. Iron core
construction is also relatively inexpensive compared with other construction types.
But iron core construction also has several disadvantages. The iron armature has a
relatively high inertia which limits motor acceleration. This construction also results in high
windinginductances which limit brush and commutator life.
In small motors, an alternative design is often used which features a 'coreless' armature
winding. This design depends upon the coil wire itself for structural integrity. As a result, the
armature is hollow, and the permanent magnet can be mounted inside the rotor coil.
Coreless DC motors have much lower armature inductance than iron-core motors of comparable
size, extending brush and commutator life/
Fig: 3.3 courtesy ofMicromole
The coreless design also allows manufacturers to build smaller motors; meanwhile, due
to the lack of iron in their rotors, coreless motors are somewhat prone to overheating. As a result,
this design is generally used just in small, low-power motors. Beamers will most often see
coreless DCmotors in the form of pager motors.
3.4 RIPPLE NUTRALIZER:
The most common meaning of ripple in electrical science, is the small unwanted
residualperiodic variation of the direct current (dc) output of a power supply which has been
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derived from an alternating current (ac) source. This ripple is due to incomplete suppression of the
alternating waveform within the power supply.
As well as this time-varying phenomenon, there is a frequency domain ripple that
arises in some classes offilterand othersignal processing networks. In this case the periodic
variation is a variation in the insertion loss of the network against increasing frequency. The
variation may not be strictly linearly periodic. In this meaning also, ripple is usually to be
considered an unwanted effect, its existence being a compromise between the amount of ripple and
other design parameters.
TIME DOMINE RIPPLE:
Full-wave rectifier circuit with a reservoir capacitor on the output for the purpose of
smoothing ripple
Ripple factor () may be defined as the ratio of the root mean square (rms) value of the
ripple voltage to the absolute value of the dc component of the output voltage, usually expressed as
a percentage. However, ripple voltage is also commonly expressed as thepeak-to-peakvalue. This
is largely because peak-to-peak is both easier to measure on an oscilloscope and is simpler to
calculate theoretically. Filter circuits intended for the reduction of ripple are usually
called smoothing circuits.
Fig: 3.4 Time domine ripple
The simplest scenario in ac to dc conversion is a rectifierwithout any smoothing
circuitry at all. The ripple voltage is very large in this situation; the peak-to-peak ripple voltage is
equal to the peak ac voltage. A more common arrangement is to allow the rectifier to work into a
large smoothing capacitorwhich acts as a reservoir. After a peak in output voltage the capacitor (C)
supplies the current to the load (R) and continues to do so until the capacitor voltage has fallen to
the value of the now rising next half-cycle of rectified voltage. At that point the rectifiers turn on
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again and deliver current to the reservoir until peak voltage is again reached. If the time constant,
CR, is large in comparison to the period of the ac waveform, then a reasonable accurate
approximation can be made by assuming that the capacitor voltage falls linearly. A further useful
assumption can be made if the ripple is small compared to the dc voltage. In this case the phase
angle through which the rectifiers conduct will be small and it can be assumed that the capacitor is
discharging all the way from one peak to the next with little loss of accuracy
Fig: 3.4 Ripple wave form
Ripple voltage from a full-wave rectifier, before and after the application of a smoothing capacitor
With the above assumptions the peak-to-peak ripple voltage can be calculated as:
For a full-wave rectifier:
For a half-wave rectification:
Where
App. is the peak-to-peak ripple voltage
Iis the current in the circuit
fis the frequency of the ac power
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Cis the capacitance
For the rms value of the ripple voltage, the calculation is more involved as the shape of the ripple
waveform has a bearing on the result. Assuming a saw tooth waveform is a similar assumption to
the ones above and yields the result:
Where
is the ripple factor
R is the resistance of the load
Another approach to reducing ripple is to use a series choke. A choke has a filtering action and
consequently produces a smoother waveform with less high-orderharmonics. Against this, the dc
output is close to the average input voltage as opposed to the higher voltage with the reservoir
capacitor which is close to the peak input voltage. With suitable approximations, the ripple factor is
given by:
Where
is the angular frequency 2f
L is the inductance of the choke
More complex arrangements are possible; the filter can be an LC ladder rather than a simple choke
or the filter and the reservoir capacitor can both be used to gain the benefits of both. The most
commonly seen of these is a low-pass-filterconsisting of a reservoir capacitor followed by a
series choke followed by a further shunt capacitor. However, use of chokes is deprecated in
contemporary designs for economic reasons. A more common solution where good ripple rejection
is required is to use a reservoir capacitor to reduce the ripple to something manageable and then
pass through a voltage regulatorcircuit. The regulator circuit, as well as regulating the output, will
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incidentally filter out nearly all of the ripple as long as the minimum level of the ripple waveform
does not go below the voltage being regulated to.
The majority of power supplies are now switched mode. The filtering requirements
for such power supplies are much easier to meet due to the frequency of the ripple waveform being
very high. In traditional power supply designs the ripple frequency is either equal to (half-wave), or
twice (full-wave) the ac line frequency. With switched mode power supplies the ripple frequency is
not related to the line frequency, but is instead related to the frequency of the chopper circuit.
The ripple frequency and its harmonics are within the audio band and will therefore be
audible on equipment such as radio receivers, equipment for playing recordings and
professional studio equipment.
The ripple frequency is within television video bandwidth. Analogue TV receivers will
exhibit a pattern of moving wavy lines if too much ripple is present.
The presence of ripple can reduce the resolution of electronic test and measurement
instruments. On an oscilloscope it will manifest itself as a visible pattern on screen.
Within digital circuits, it reduces the threshold, as does any form of supply rail noise, at
which logic circuits give incorrect outputs and data is corrupted.
High amplitude ripple currents reduce the life ofelectrolytic capacitors.
Fig:3.4 Ripple on a fifth order prototype Chebyshev filter
Ripple in the context of the frequency domain is referring to the periodic variation
in insertion loss with frequency of a filter or some othertwo-port network. Not all filters exhibit
ripple, some have monotonically increasing insertion loss with frequency such as the Butterworth
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filter. Common classes of filter which exhibit ripple are the Chebyshev filter, inverse Chebyshev
filterand the Elliptical filter. The ripple is not usually strictly linearly periodic as can be seen from
the example plot. Other examples of networks exhibiting ripple are impedance matching networks
that have been designed using Chebyshev polynomials. The ripple of these networks, unlike regular
filters, will never reach 0dB at minimum loss if designed for optimum transmission across the pass
band as a whole.
The amount of ripple can be traded for other parameters in the filter design. For instance, the rate
ofroll-offfrom thepass band to the stop band can be increased at the expense of increasing the
ripple without increasing the order of the filter (that is, the number of components has stayed the
same). On the other hand, the ripple can be reduced by increasing the order of the filter while at the
same time maintaining the same rate of roll-off.
3.5RECHARGEBLE BATTERIES
A rechargeable battery or storage battery is a group of one or more electrochemical
cells. They are known as secondary cells because their electrochemical reactions are electrically
reversible. Rechargeable batteries come in many different shapes and sizes, ranging anything froma button cell to megawatt systems connected to stabilize an electrical distribution network. Several
different combinations of chemicals are commonly used, including: lead-acid, nickel
cadmium(NiCad), nickel metal hydride (Nigh), lithium ion (Li-ion), and lithium ion polymer(Li-ion
polymer).
Fig: 3.5 Rechargeable Batteries
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Rechargeable batteries have lower total cost of use and environmental impact than
disposable batteries. Some rechargeable battery types are available in the same sizes as disposable
types. Rechargeable batteries have higher initial cost, but can be recharged very cheaply and used
many times.
Rechargeable batteries are used forautomobile starters, portable consumer devices, light
vehicles (such as motorized wheelchairs, golf carts, electric bicycles, and electric forklifts), tools,
anduninterruptible power supplies. Emerging applications in hybrid electric vehicles and electric
vehiclesare driving the technology to reduce cost and weight and increase lifetime. Normally, new
rechargeable batteries have to be charged before use; newerlow self-discharge batteries hold their
charge for many months, and are supplied charged to about 70% of their rated capacity.
Grid energy storage applications use rechargeable batteries for load leveling, where
they store electric energy for use during peak load periods, and for renewable uses, such as storing
power generated fromphotovoltaic arrays during the day to be used at night. By charging batteries
during periods of low demand and returning energy to the grid during periods of high electrical
demand, load-leveling helps eliminate the need for expensivepeaking power plants and
helpsamortize the cost of generators over more hours of operation.
The USNational Electrical Manufacturers Association has estimated that U.S. demand
for rechargeable batteries is growing twice as fast as demand for non -rechargeable.
CHARGING AND DISCHARGING
During charging, the positive active material is oxidized, producing electrons, and the
negative material isreduced, consuming electrons. These electrons constitute thecurrent flow in the
external circuit. The electrolyte may serve as a simple buffer forion flow between the electrodes, as
inlithium-ion and nickel-cadmium cells, or it may be an active participant in
the electrochemical reaction, as inlead-acid cells.
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Fig: 3.5 charging of a secondary cell battery. Fig: 3.5 Battery charger
Fig: 3.5 A solar-powered charger for rechargeable batteries
The energy used to charge rechargeable batteries usually comes from abattery chargerusing
AC mains electricity. Chargers take from a few minutes (rapid chargers) to several hours to charge a
battery. Most batteries are capable of being charged far faster than simple battery chargers are
capable of; there are chargers that can charge consumer sizes of NiMH batteries in 15 minutes. Fast
charges must have multiple ways of detecting full charge (voltage, temperature, etc.) to stop
charging before onset of harmful overcharging.
Rechargeable multi-cell batteries are susceptible to cell damage due to reverse
charging if they are fully discharged. Fully integratedbattery chargers that optimize the charging
current are available.
Attempting to recharge non-rechargeable batteries with unsuitable equipment may
causebattery explosionFlow batteries, used for specialised applications, are recharged by replacing
the electrolyte liquid.
Battery manufacturers' technical notes often refer to VPC; this is volts percell, and
refers to the individual secondary cells that make up the battery. For example, to charge a 12 V
battery (containing 6 cells of 2 V each) at 2.3 VPC requires a voltage of 13.8 V across the battery's
terminals.
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Non-rechargeable alkaline and zinc-carbon cells output 1.5V when new, but this
voltage gradually drops with use. Most NiMH AA and AAA batteries rate their cells at 1.2 V, and
can usually be used in equipment designed to use alkaline batteries up to an end-point of 0.9 to 1.2V
Reverse charging:Subjecting a discharged cell to a current in the direction which tends to discharge it
further, rather than charge it, is called reverse charging; this damages cells. Reverse charging can
occur under a number of circumstances, the two most common being:
When a battery or cell is connected to a charging circuit the wrong way round.
When a battery made of several cells connected in series is deeply discharged.
When one cell completely discharges ahead of the rest, the live cells will apply a reverse current tothe discharged cell ("cell reversal"). This can happen even to a "weak" cell that is not fully
discharged. If the battery drain current is high enough, the weak cell's internal resistance can
experience a reverse voltage that is greater than the cell's remaining internal forward voltage. This
results in the reversal of the weak cell's polarity while the current is flowing through the cells. [3]
[4] this can significantly shorten the life of the affected cell and therefore of the battery. The higher
the discharge rate of the battery needs to be, the better matched the cells should be, both in kind of
cell and state of charge. In some extreme cases, the reversed cell can begin to emit smoke or catch
fire.
In critical applications using Ni-Cad batteries, such as in aircraft, each cell is individually
discharged by connecting a load clip across the terminals of each cell, thereby avoiding cell
reversal, then charging the cells in series.
3.6 INVERTER
An inverter is an electrical device that converts direct current (DC) to alternating
current (AC); the converted AC can be at any required voltage and frequency with the use of
appropriate transformers, switching, and control circuits. Solid-state inverters have no moving parts
and are used in a wide range of applications, from small switching power supplies in computers, to
large electric utilityhigh-voltage direct current applications that transport bulk power. Inverters are
commonly used to supply AC power from DC sources such as solar panels orbatteries.
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Fig: 3.6 Inverter
There are two main types of inverter. The output of a modified sine wave inverter is similar
to a square wave output except that the output goes to zero volts for a time before switching positive
or negative. It is simple and low cost (~$0.10USD/Watt) and is compatible with most electronic
devices, except for sensitive or specialized equipment, for example certain laser printers. A pure
sine wave inverter produces a nearly perfect sine wave output (
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Fig:3.6 Inverter snap
An inverter converts the DC electricity from sources such as batteries, solar panels,
orfuel cells to AC electricity. The electricity can be at any required voltage; in particular it can
operate AC equipment designed for mains operation, or rectified to produce DC at any desired
voltage. Grid tie inverterscan feed energy back into the distribution network because they produce
alternating current with the same wave shape and frequency as supplied by the distribution system.
They can also switch off automatically in the event of ablackout. Micro-inverters convert direct
current from individual solar panels into alternating current for the electric grid. They are grid tie
designs by default.
Uninterruptible power supplies:
Anuninterruptible power supply (UPS) uses batteries and an inverter to supply AC
power when main power is not available. When main power is restored, a rectifiersupplies DC
power to recharge the batteries.
Induction heating:
Inverters convert low frequency main AC power to higher frequency for use in induction
heating. To do this, AC power is first rectified to provide DC power. The inverter then changes the
DC power to high frequency AC power.
HVDC power transmission:
With HVDC power transmission, AC power is rectified and high voltage DC power is
transmitted to another location. At the receiving location, an inverter in a static inverter
plant converts the power back to AC.
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Variable-frequency drive :
Avariable-frequency drive controls the operating speed of an AC motor by controlling
the frequency and voltage of the power supplied to the motor. An inverter provides the controlled
power. In most cases, the variable-frequency drive includes a rectifierso that DC power for theinverter can be provided from main AC power. Since an inverter is the key component, variable-
frequency drives are sometimes called inverter drives or just inverters.
Electric vehicle drives:
Adjustable speed motor control inverters are currently used to power the traction
motors in someelectric and diesel-electric rail vehicles as well as somebattery electric
vehiclesand electric highway vehicles such as theToyota Pries and Frisker Karma. Various
improvements in inverter technology are being developed specifically for electric vehicle
applications.[2] In vehicles withregenerative braking, the inverter also takes power from the motor
(now acting as a generator) and stores it in the batteries.
Air conditioning :
An air conditionerbearing the inverter tag uses a variable-frequency drive to control the
speed of the motor and thus the compressor.
The general case:Atransformerallows AC power to be converted to any desired voltage, but at the same
frequency. Inverters, plus rectifiers for DC, can be designed to convert from any voltage, AC or DC,
to any other voltage, also AC or DC, at any desired frequency. The output power can never exceed
the input power, but efficiencies can be high, with a small proportion of the power dissipated as
waste heat.
Basic designs:
In one simple inverter circuit, DC power is connected to a transformerthrough the centre
tap of the primary winding. A switch is rapidly switched back and forth to allow current to flow
back to the DC source following two alternate paths through one end of the primary winding and
then the other. The alternation of the direction of current in the primary winding of the transformer
produces alternating current (AC) in the secondary circuit.
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