2nd wangener automotive symposium inverter trends ... · 11/7/2019 · consideration of the...

Antoine Tan-Kim, Markus Preuss

AVL Software and Functions GmbH

Confidential

2nd Wangener Automotive Symposium

Inverter Trends & Technology (7th November 2019)

Focus on Specific Topics in Electromagnetic and Thermal E-Motor Design – Part EMAG

Antoine Tan-Kim, Markus Preuss | E-Machine | 07 November 2019 | 2Confidential

Agenda

• AVL SFR e-machine development

• Challenges in e-machine development

• Losses in e-machine

• Focus on AC losses

• Focus on iron and permanent magnet losses

• Influence of the inverter switching frequency on the machine losses

• Conclusion and next steps


AVL E-Drive Development (1/2)


AVL E-Drive Development (2/2)

Part I: Focus on the e-machine losses and the influence of the inverter on theses losses Part II: Focus on the thermal behavior of the e-machine

DRIVE

EMAG

MECHTHERM

NVH

➔n, T, Iph

➔Tpp, forces Drive line NVH ➔

EV NVH

CFD

➔n, T, Ploss

E-drive cooling ➔Vehicle cooling ➔

EV TH

Driving cycles & usage profile ➔


Challenges of E-Machine Development

Focus on 3 main challenges:• Machine losses• Machine cooling

• Influence of the inverter switching frequency

AVL HIGH-SPEED E-AXLE

▪ 800 V technology

▪ Dual motor & dual transmission = torque vectoring

▪ High power density

▪ E-Motor with direct oil cooling to boost performance

▪ Dual SiC-inverter, common DC-Link & interleaving


Losses in E-Machine

Distribution of the losses in a “typical” IPMSM for automotive traction application:

• Copper DC Joule losses

• Copper AC Joule losses ~f and f²

• Eddy current losses ~f²

• Hysteresis losses ~f

• Excess losses ~f1.5

• Eddy current losses ~f²• Bearing losses ~ f

• Windage losses ~ f²

AC losses, iron losses and permanent magnet losses are all frequency-dependent (~f & f²) and cannot be easily separated. Which parameters influence these losses and how can we

calculate them?


Focus on AC Losses (1/2)

AC losses are not only dependent on the frequency. The position of the wires in the slot, the phase advance angle, the temperature and the current amplitude also influence AC losses.

• AC losses are frequency dependent copper losses due to skin and proximity effect. • Which other factors influence these AC losses?

• Position of the wires in the slot and connection of the windings

• Temperature• Phase advance angle • Current amplitude


Optimal phase advance angle trajectory

Real trajectory Over-estimationUnder-estimation

Focus on AC Losses (2/2)

Phase resistance over the torque-speed operating space

Torq

ue [

Nm

]

Rotation speed [rpm]

With wrong assumptions on, for instance, phase advance angle when deriving AC/DC resistance ratio, the results can be either over or under estimated.


Focus on Iron and Permanent Magnet Losses

Iron losses can be determined based on measured material data. The influence of the manufacturing

process (e.g. cutting process) is difficult to simulate and also requires experimental data.

Magnet losses can be determined with the help of 3D FEM simulations. Magnets can be

segmented to reduce the losses.

0 0,5 1 1,5 2

Specific

iro

n losses [

W/k

g]

Magnetic flux density [T]

50 Hz 400 Hz 2500 Hz 5000 Hz 10000 Hz

Iron losses vs. magnetic flux density and frequency

Eddy currents in segmented interior permanent magnets


Influence of Inverter Switching Frequency on Iron and Permanent Magnet Losses

0,0

2,0

4,0

6,0

8,0

10,0

12,0

5 10 15 20

Inverter switching frequency (kHz)

Ratio of magnet losses with

PWM to magnet losses with

sinusoidal current vs. inverter

switching frequency

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

5 10 15 20

Inverter switching frequency (kHz)

Ratio of iron losses with PWM to

iron losses with sinusoidal

current vs. inverter switching

frequency

Influence of the inverter switching frequency on the frequency dependent losses of an electrical machine?• Almost no influence on the iron losses

• Significant influence on the permanent magnet losses

PMSM, fundamental frequency 450 Hz

Curr

ent

Time

Phase currents with

PWM


Conclusion and Next Steps

• The accurate simulation of the machine thermal behavior starts with the accurate simulation of themachine losses.

• More and more influencing factors can now be considered with the help of FEM simulations.

• AC losses are not only dependent on the frequency but also on the position of the wires in the slot,the phase advance angle, the temperature and the current amplitude.

• Compared to sinusoidal currents, “real” currents including PWM effects result in significantly higheriron and permanent magnet losses.

• The influence of the inverter switching frequency on the AC losses will also be investigated in afuture study.

Antoine Tan-Kim, Markus Preuss

AVL Software and Functions GmbH

Confidential

2nd Wangener Automotive Symposium

Inverter Trends & Technology (7th November 2019)

Focus on Specific Topics in Electromagnetic and Thermal E-Motor Design – Part THERMAL


Agenda

• Main influences on e-machine cooling

• Definition of the thermal capability of the e-machine

• Continuous operation

• Peak operation

• Consideration of the thermal overall behavior


Main Influences on E-Machine Cooling

• E-machine type

• Field of application (operation conditions)

• Operation requirements

• Losses and loss distribution

• Cooling architecture

• Available coolants and cooling interfaces

• Coolant conditions

• E-machine materials (performance vs. costs)

• …

Free ConvectionDirect Oil

Oil Spray Forced ConvectionOutside

JacketCooling

Forced ConvectionInside

Creation of a suitable cooling system


Definition of the Thermal Capability of theE-Machine

What does this mean for the thermal capability of the machine?

➢ Is it necessary that the e-machine can be operated continuously within the whole “continuous” region (S1 performance)?

➢ What are the demands for the “peak” operation of the machine?

➢ How critical is the thermal behavior at single operation points in comparison with the thermal behavior at real duty cycle operation?

➢ Are the defined thermal requirements suitable for the application?

➢ …

Torque

Speed

PEAKCONT

Basicregion

Fieldweakening

region

Based on the given requirements ane-machine is designed by the electromagnetic designer that fulfills the needed performance.

From the electromagnetic side this machine can have a characteristic as following


Definition of the Thermal Capability of theE-Machine – Continuous Operation

S1 means the torque-speed curve where the thermal steady state condition is reached, up to the thermal limitations of the e-machine, mainly of the winding temperature level.

For automotive applications that time will normally not be reached and therefore the definition of S1 for continuous operation is not suitable*.

Is it necessary that the e-machine can be operated continuously within the whole “continuous” region (S1 performance)?

Temp

Time

Max. allowed winding

temperature e.g. 180°C

Real continuous e.g. > hours

Thermal steady state

*Example forthermal continuousregion! E.g. required time

30 minutes

Torque

Speed

PEAKCONT

Dependent on the needs of the application a

continuous operation in this region might not be

necessary.


Definition of the Thermal Capability of theE-Machine – Continuous Operation

The relevant criteria for the continuous operation definition usually are:

• Continuous values for torque and power

• Start temperature conditions

• Times for continuous performance capabilities

• Coolant inlet temperature and flow rate

• Environmental conditions

Is it necessary that the e-machine can be operated continuously within the whole “continuous” region (S1 performance)?

In case that a required time for continuous operation is

defined the starting conditions become relevant!


Definition of the Thermal Capability of theE-Machine – Peak Operation

Peak operation starting from a steady state condition:

If this is required, then a temperature reserve gap between continuous end condition and peak end condition has to be available.

In this case an identical repeatability of the peak performance operation is possible when cooling down again to the former steady state condition of the continuous operation point.

What are the demands for the “peak” operation of the machine?

Temp

Time

Temperature <

max. allowed

continuous

Peak operation time

Max. allowed temperature

e.g. 180°C temp reserve gap

Temp

Time

Temperature <

max. allowed

continuous

Peak operation time


e.g. 180°C

Time for cool down


Definition of the Thermal Capability of theE-Machine – Peak Operation

Peak operation starting from a defined temperature level (no temperature reserve gap):

If this is required, then no identical repeatability of peak performance operation is possible when cooling down by decreasing the load back to the continuous condition.

For identical repeatability the cool down has to go to the original starting conditions of the first peak operation. That is only possible when using a load that is smaller than the initial continuous condition.

What are the demands for the “peak” operation of the machine?

Temp

TimeReal

continuous e.g. > hours

„Continuous“-time, e.g.10min/15min/30min


e.g. 180°C

Temperature <

max. allowed

Peak1 operation time


Peak2 operation

time=

Peak1 operation

time

Temp

TimeReal




e.g. 180°C

Temperature <

max. allowed



Peak2 operation

time<

Peak1 operation

time

Temp

TimeReal




e.g. 180°C

Temperature <

max. allowed



Peak2 operation

time<

Peak1 operation

time

Temp

TimeReal




e.g. 180°C

Temperature <

max. allowed



Peak2 operation

time<

Peak1 operation

time


Consideration of the Thermal Overall Behavior

For a first check of the thermal behavior of the e-machine defined operation points, “continuous” and “peak”, are considered dependent on the existing thermal requirements.

In case that appropriate duty cycle data are defined by the customer, or a standard duty cycle was selected, additional duty cycle considerations are done to check the overall behavior of the machine under realistic conditions.

Definitionby

Costumer

If nototherwise

defined

T(t) n(t)

The needed e-machine characteristic is dependent on conditions like e.g. the needed gradeability at a defined vehicle

speed and so on…


Consideration of the Thermal Overall Behavior

Based on the results from the:

it is then checked if:

• the winding temperature stays within a sufficient range to fulfill the required lifetime→ E.g.: A winding with insulation class H would have a lifetime of about 20.000h if it would be

operated constantly at its reference temperature of 180°C

• the magnet temperature stays below its temperature limit to avoid demagnetization of the magnets

If these criteria are fulfilled the thermal design is ok, if not adjustments from the design have to be done.

Transient analysis for“Continuous” operation points

Transient analysis for“Peak” operation points

Duty Cycle analysis

Example: PSM (permanent magnet synchronous machine)

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Thank You

2nd wangener automotive symposium inverter trends ... · 11/7/2019 · consideration of the...

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