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© EVS-25 Shenzhen, China, Nov. 5-9, 2010
The 25th World Battery, Hybrid and Fuel Cell Electric Vehicle Symposium & Exhibition
Saphir Faid1 , Patrick Debal1 , and Steven Bervoets1
1Punch Powertrain, R&D Department, Schurhovenveld 4 125, BE3800 Sint-Truiden, Belgium
Professor: Ming-Shyan Wang
Student: Zong-Ren Yang
ID Number:4A02C071
+ Electric motor is key part in electric vehicles including hybrid electric
vehicle, fuel cell electric vehicle and battery electric vehicle. Wide
torque-speed range and high reliability are needed of the motor
applied in electric vehicles. Novel hybrid switched reluctance motor
is developed. It combines features of robust as switched reluctance
motor and that of high efficiency of permanent magnet motor. Flux
strengthening and weakening control give large maximum torque
and high speed to the motor drives. They are implemented by only
simply controlling the magnitude and direction of the current in an
additional coil in the motor. Rotor position is detected by the signal
from stationary coils in the motor and rotor speed is calculated
according to this signal. To test characteristics of the motor drives, an
experimental bench is developed. It is easy to test four quadrants
torque-speed and dynamic characteristics of the motor drives. The
whole testing system is energy saving.
Punch Powertrain develops hybrid and electric drivetrains for
passenger cars. The electric traction motor is a crucial component
as it impacts the vehicle’s performance and because the cost of
batteries related to range requirements urges for a highly efficient
but costeffective drivetrain. For the projects under development,
several options for electric traction motors were investigated,
namely permanent magnet motors, induction motors and switched
reluctance motors (SRM). Induction motors are the most widely
used type in industrial applications as well as heavy traction
applications (railway, electric buses,…). Permanent magnet
synchronous motors offer significantly better efficiency and power
density, which has led to increasing popularity in hybrid and electric
passenger cars, electric bicycles, scooters,… However, cost and
supply concerns regarding the limited reserves of rare earth
magnets are a limiting factor for application of permanent magnet
motors in a scenario of serious worldwide electrification of mobility
. The topic on the most suitable electric machine remains open, and
because of some particular advantages, switched reluctance motors
may offer an interesting solution for applications requiring a highly
performing but cost-effective solution.
+ Based on vehicle performance simulations for a hybrid vehicle , the
following specifications were targeted for this electric motor design:
Peak Torque: 200 Nm
Peak Power: 30 kW
Speed Range: 0-10 000 rpm
Continuous Power: 15 Kw
In order to achieve optimal integration into the hybrid powertrain
package developed by Punch Powertrain , the following
dimensional constraints were set:
Diameter: 225 mm
Length: 275 mm
+ A switched reluctance motor produces
torque purely through interaction of the
stator field with rotor saliency. The basic
operation of a switched reluctance motor is
illustrated. The stator consists of laminated
iron with stator poles and windings. The
rotor is just laminated iron. By exciting a
pair of opposing stator windings, the
principle of reluctance will cause a torque to
align the rotor poles with the stator poles.
The simplest design can be a single phase
motor, but thiswould not allow total control
of the motor. The shown design is an 8/6
configuration with 8 stator poles and 6 rotor
poles which is a typical four phase motor.
The four phase operation offers the
possibility to achieve full torque in each
rotor position and allows smoothening of
torque ripple at low speeds a demonstrated
in this paper.
+ The manufactured prototypes were validated
on a test rig with full measurement
equipment such as a torque measurement
device for accurate characterization. The
characterization on the test rig allowed more
precise determination of the efficiency map
and actual torque delivered by the motor.
During characterization on the test bench,
these calculated control parameters were
tested to deliver the requested torque and
efficiency. After optimization of the control
parameters, the final torque-speed map was
determined, the ‘fingerprint’ of the motor
from a vehicle point of view. As visible on
figure , the motor actually delivers higher
peak power at medium speeds and achieves
efficiency in excess of 90% (motor +inverter)
in a wide speed range.
+
After characterization the motor was integrated with the other subsystems into a
complete parallel hybrid powertrain as illustrated in figure The powertrain was
then implemented into test vehicles where performance and drivability could be
assessed . During the first assessment, torque ripple was investigated and brought
to an acceptable level for comfortable driving, even at low speeds. The motor
performance was fulfilling its expectations delivering the requested torque
precisely, and demonstrating reliability. Regarding NVH aspects there were no
issues with motor vibrations transmitted to the vehicle, and the acoustic noise
produced by the motor itself although clearly perceivable at low speeds especially
in generating mode, seemed acceptable to most of the users (subjective
assessment). It must me noted that controls parameters obviously have a
significant impact on acoustic noise as well, and that this is also part of the overall
compromise in optimizing the excitation parameters. Another point to note is the
fact that the power electronics unit in this case was also a source of acoustic noise
and was perceived as more annoying to the users due to the high pitch noise
related to the switching frequency of the IGBT modules. However this is something
which can be improved by better sealing of the housing of the power electronics
unit, positioning of this unit in the vehicle and by shifting the switching
frequencies (although the last aspect is related to switching losses and hence to
inverter efficiency).
Integration to hybrid powertrain through chain drive
Complete hybrid powertrain and test vehicle
+ The conducted motor design and optimization has proven
successful with regard to delivered torque and efficiency. The
issue of torque ripple, which could be a major drawback for
traction applications, was successfully addressed by use of a
four phase design and application of current profiling. The
integration into test vehicles allowed assessment in the actual
application, and first subjective assessments by various test
users were positive, although these are subjective results,
more objective measurements are to be carried out. The
operational test vehicles are nevertheless an illustration of the
potential of this low-cost technology. The positive feedback,
ideas for even better design and control, and availability of
options for noise handling offer further room for improvement.
Hence, Punch Powertrain will build on this experience and
come up with an even more performing solution.
+ [1] Oakdene Hollins, Lanthanide Resources and Alternatives,
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http://www.oakdenehollins.co.uk, March 2010
[2] R.S. Colby et.al. Vibrating modes and acoustic noise in a 4 phase
switched reluctance motor. Conference Record of the 1995 IEEE, 1:441–
447, 1995.
[3] D.E. Cameron et.al. The origin and reduction of acoustic noise in a
doubly salient variarable-reluctance machine. IEEE Transactions on
Industry Applications, 28:1250–1255, 1992.
[4] C. Pollock et.al. Acoustic noise cancellation technique for switched
reluctance drives. IEEE Transactions on Industry Applications, 33:477–484,
1997.
[5] T.J.E. Miller. Switched reluctance motors and their control. Magna
Physics Publishing, New York, 1993.
[6] D’hulster F., Stockman K., Belmans R., Modeling of switched reluctance
machines: state of the art, International Journal of Modelling and
Simulation, Vol. 24, No 4, 2004, pp. 216-223.
[7] P. Debal et.al. Development of a Post-Transmission Hybrid Powertrain,
EVS24, May 13-16, 2009, Stavanger, Norway
[8] Rasmussen et.al. Structural Stator Spacers - The key to silent electrical
machines, March-April 2004, IEEE Transactions on Industry Applications,
Issue 2, p574 - 581