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Robot and Servo Drive Lab.
A Permanent Magnet Integrated Starter Generator for
Electric Vehicle Onboard Range Extender Application
Can-Fei Wang , Meng-Jia Jin , Jian-Xin Shen , and Cheng Yuan
Department of Electrical Engineering, Zhejiang University, Hangzhou 310027, China
Wujiang Nanyuan Electric Appliance Co., Ltd., Suzhou 215231, China
IEEE TRANSACTIONS ON MAGNETICS, VOL. 48, NO. 4, APRIL 2012 1625 -1628
Adviser: Ming-Shyan Wang
Student: Cian-Yong Fong
Student ID: MA120215
Department of Electrical Engineering
Southern Taiwan University
2016/7/14
Outline
1.Abstract
2.Introduction
3. Proposed Machine Structures
4. Eddy Current Losses
a. Sleeve on SPM Rotor
b. Short Circuit Rings Around Magnets on SPM Rotor
c. Axial Segmental Sleeves on SPM Rotor
d. Short Circuit Rings Around Magnets on IPM Rotor
5. Experiment Results
6. Cost Evaluation
7. Conclusions
8. References
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Department of Electrical Engineering
Southern Taiwan University
Robot and Servo Drive Lab.
Abstract
This paper deals with a permanent magnet (PM) brushless machine used for
integrated starter generator (ISG) in an electric vehicle (EV) onboard range
extender (ORX).
ISGs with both surface-mounted PM (SPM) and interior PM (IPM) rotors
have been developed for comparatively analysis.
Some techniques for eddy current loss reduction are discussed, while influence
of the rotor protecting sleeve material and thickness, axial segmental sleeves,
and short circuit rings (ShCRs) around each magnet are particularly
investigated.
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Southern Taiwan University
Robot and Servo Drive Lab.
Introduction
In this paper, finite element method (FEM) is used for design and analysis of
the ISG. Different stator-slot/rotor-pole combinations and rotor structures are
analyzed. Especially, the eddy current loss and fixation method of magnets
are comparatively studied for both surface-mounted PM (SPM) and interior
PM (IPM) types.
Some different techniques for the magnet fixation with low eddy current loss
are analyzed. Subsequently, two 12-slot/10-pole ISG prototypes, with SPM
and IPM rotors, respectively, are built for experimental validation.
Furthermore, the cost is also evaluated, taking both material and manufacture
cost into account. In conclusion, both SPM and IPM ISGs satisfy the
requirements, while the IPM ISG has a slightly lower efficiency as well as
lower cost.
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Proposed Machine Structures
TABLE II
KEY PARAMETERS OF THE PROPOSED MACHINE
Fig. 1. ISG configurations, (a) SPM, and (b) IPM.
Optimizations based on FEM have been carried out. The proposed ISG
machines with both SPM and IPM rotors are shown in Fig. 1 and the key
parameters are listed in Table II.In the IPM rotor the laminated core can
enclose the magnets by themselves, while in the SPM rotor an additional
sleeve is need. The sleeve has to be dealt with cautiously in both
electromagnetic design and manufacture process.
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Southern Taiwan University
Robot and Servo Drive Lab.
Proposed Machine Structures
Fig. 6. Short circuit rings (ShCR) around magnets in IPM.
To reduce the flux leakage, thinner bridge is preferred. However, the bridge
should be thick enough to guarantee the mechanical strength, considering the
significant centrifugal force when the machine operates at high speed. Usually,
magnetic saturation occurs on the bridge rather than on the rib, which is
between the two adjacent poles to support the bridge.
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Southern Taiwan University
Robot and Servo Drive Lab.
Sleeve on SPM Rotor
A major consideration for the sleeve is its eddy current loss, which is
associated with the electrical conductivity. Different nonmagnetic materials
are comparatively analyzed, including copper, stainless steel and fiberglass.
Their electrical conductivity is listed in Table III. Their skin depth when the
machine runs at the maximum speed of 4500 rpm is also given in Table III.
TABLE III
PHYSICAL PARAMETERS OF SLEEVE MATERIALS
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Sleeve on SPM Rotor
Fig. 2. Eddy current losses in both magnets and different sleeves.
Obviously, fiberglass sleeve is the best in terms of minimum eddy current loss.
However, the thermal expansion of fiberglass is quite different from that of the
magnets and rotor core. Due to the considerable temperature rise of the rotor
when running at high speed, the fiberglass might be broken as a result of the
different thermal expansion. Thus, fiberglass is not preferred to serve as the
sleeve.
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Robot and Servo Drive Lab.
Sleeve on SPM Rotor
TABLE III
PHYSICAL PARAMETERS OF SLEEVE MATERIALS
Fig. 2. Eddy current losses in both magnets and different sleeves.
This is related to the material skin depth. As can be seen from Table III, the
skin depth of both copper and stainless steel is much larger than the
investigated sleeve thickness in Fig. 2, hence, eddy current exists in the
whole thickness of the sleeve. Therefore, the thinner the sleeve is, the lower
the eddy current loss.
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Southern Taiwan University
Robot and Servo Drive Lab.
Short Circuit Rings Around Magnets on
SPM Rotor
Fig. 3. Short circuit rings (ShCR) around magnets in SPM.
In it is proposed to add a short circuit ring (ShCR) around each magnet, as
shown in Fig. 3, so as to reduce the eddy current loss in the rotor. Such
ShCRs are also examined in this project. Theoretically, the induced currents
caused by the flux linkage variation in the ShCR would build an inverted
magnetic field to prevent the flux variation. And, the decreased flux
variation would also result in eddy current loss reduction in the magnets.
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Department of Electrical Engineering
Southern Taiwan University
Robot and Servo Drive Lab.
Short Circuit Rings Around Magnets on
SPM Rotor
Fig. 4. Comparison of losses with or without sleeve or ShCR in SPM rotor.
When both “sleeve and ShCR” are employed, their influence on the eddy
current loss cancels each other. Apparently, the ShCR plays a remarkable role
to reduce the eddy current loss. However, it suffers from a considerable ohmic
loss due to its extremely large short circuit current. This is also evident in
Fig. 4. Therefore, considering the overall losses and the rotor mechanical
strength, the stainless sleeve is essential while the ShCR is not employed.
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Southern Taiwan University
Robot and Servo Drive Lab.
Axial Segmental Sleeves on SPM Rotor
Fig. 5. Prototype SPM rotor, (a) without sleeve, and (b) with
two axially segmental sleeves.
As analyzed earlier, the thinner sleeve produces the less eddy current loss.
However, the radial thickness of the sleeve has to be large enough to contain the
magnets safely at hgih rotary speed. By other means, the sleeve could be
separated into some shorter sleeves in axial direction.
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Robot and Servo Drive Lab.
Short Circuit Rings Around Magnets on
IPM Rotor
Fig. 7. Comparison of losses with or without ShCR in IPM rotor.
Fig. 8. Prototype IPM machine, (a) IPM rotor, and (b) IPM
rotor and nonoverlapping winding stator.
Clearly, by using the ShCR, the eddy current loss is drastically decreased by
90%, viz., from 202W to 18W. However, much more extra ohmic loss exists in
the ShCR, so that the total loss of the case “with ShCR” is about 65% higher
than that with the “original” IPM rotor. Therefore, the ShCR is not adopted in
this application.
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Southern Taiwan University
Robot and Servo Drive Lab.
Experiment Results
Fig. 9. Prototype ISG, (a) ISG alone, and (b) ICE-ISG unit.
Fig. 10. Phase current during operations in (a) starter mode,
and (b) generator mode.
The speed in Fig. 10(a) is about 340 rpm, and only two phases of
currents are illustrated. Variation of current amplitude reveals that the
ICE shaft torque changes in a rotation cycle. When the speed was above
800 rpm, the ISG was turned off and the ICE was run by fuel. The ISG
did not work as a generator until the ICE run over the speed of 4000 rpm.
Fig. 10(b) demonstrates the phase current waveform at 4800 rpm with a
peak value of 47 A.
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Robot and Servo Drive Lab.
Cost Evaluation
The main cost saving for the IPM rotor is the magnet cost. Although more magnets
are employed in the IPM rotorthan in the SPM rotor, the IPM rotor uses block
magnets while the SPM rotor uses tile-shaped magnets, and the former are 20%
cheaper per unit weight than the latter. Moreover, the sleeve also increases the cost
of the SPM rotor.
TABLE IV
COST COMPARISON (UNIT: CNY)
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Conclusions
It has also been observed that the thinner the sleeve is, the less eddy current
loss exists as long as the skin depth is larger than the sleeve thickness.
Furthermore, axially segmenting the sleeve can reduce the eddy current loss
effectively, while the short circuit rings (ShCRs) around magnets can reduce
the eddy current loss but meanwhile bring significant ohmic loss.
Both SPM and IPM machines can satisfy the requirements, while the IPM
machine has a relatively lower cost as well as lower efficiency.
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References
[1] T. B. Gage, SAE Int. 1997, Paper Number: 972634.
[2] M. Barcaro, L. Alberti, A. Faggion, L. Sgarbossa, M. Dai Pre, N. Bianchi, and S. Bolognani, “IPM machine drive
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Edmonton, Canada, Oct. 2008.
[3] M. Yoneda, M. Shoji, Y. Kim, and H. Dohmeki, “Novel selection of the slot/pole ratio of the PMSMfor auxiliary
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[4] N. Bianchi, S. Bolognani,M. D. Pre, and G. Grezzani, “Design considerations for fractional-slot winding
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[5] G. Ombach and J. Junak, “Two rotors designs’ comparison of permanent magnet brushless synchronousmotor for
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Conf. Rec. IEEE IAS Annu. Meeting, New Orleans, LA, Sep. 23, 2007.
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References
[8] J. X. Shen, C. F. Wang, D. M. Miao, M. J. Jin, D. Shi, and Y. Wang, “Analysis and optimization of a modular
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[9] J. D. Ede, K. Atallah, G. W. Jewell, J. B. Wang, and D. Howe, “Effect of axial segmentation of permanent
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pp. 1703–1708.
[10] Z. Q. Zhu, K. Ng, N. Schofield, and D. Howe, “Improved analytical modeling of rotor eddy current loss in
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Appl., vol. 151, no. 6, pp. 641–650, Nov. 2004.
[11] D. Ishak, Z. Q. Zhu, and D. Howe, “Rotor eddy current loss in PM brushless machines with fractional slot
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[12] J. Wang, K. Atallah, R. Chin, W. M. Arshad, and H. Lendenmann, “Rotor eddy-current loss in permanentmagnet brushless AC machines,” IEEE Trans. Magn., vol. 46, no. 7, pp. 2701–2707, Jul. 2010.
[13] F. Z. Zhou, J. X. Shen, W. Z. Fei, and R. G. Lin, “Study of retaining sleeve and conductive shield and their
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Oct. 2006.
[14] N. Bianchi, S. Bolognani, and A. Faggion, “A ringed-pole SPM motor for sensorless drives-electromagnetic
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