EVS28
KINTEX, Korea, May 3-6, 2015
Current control strategy of Wound Rotor Synchronous
Machine with losses consideration
Qi Wang1, Heon-Hyeong Lee, Hong-Joo Park, Kyu-Sung Park, Geun-Ho Lee
Graduate School of Automotive Engineering, Kookmin University,
861-1 Jeongneung-Dong, SeongBuk-Gu, Seoul 136-702, South Korea
E-mail: arsenal@kookmin.ac.kr
motor@kookmin.ac.kr
Abstract
Wound rotor synchronous machine (WRSM) could be a challenger to displace the interior permanent
magnetic synchronous machine (IPMSM) due to plentiful merits of WRSM such as high starting toque at
low speed range, good performance in flux weakening region, freedom field control via external circuit
current without permanent magnet and power factor be controllable by field current. Inversely, there are
also some drawbacks existing, which the exciting current should be injected via a slip ring so that external
circuit makes the entire circuits more complex and shrink the life cycle. Also EMI and EMC occurred due
to the outer circuit. In particular, field current are controllable, this study present a strategy that can be
reasonable collocate the stator and field current for flux weakening control, so that the losses are able to reduced
to maximize the efficiency. In addition, nonlinear variables are taken into account such as d-q axes inductances
and phase flux linkage for accuracy. This algorithm is deemed to be Belt-driven Starter Generator (BSG) to
serve for HEV e-Assisted application. A 6kw WRSM involve the current control strategy show the well
performances such as the efficiency in the motoring mode and power regeneration as generator. The validity of
the proposed algorithm has been verified by experimental results.
Keywords: Maximum efficiency, field current control, flux weakening control, BSG
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Introduction
WRSM is able to be served for HEV Belt-driven
Starter Generator (BSG) as e-Assisted application
due to its merits, thereby the high efficiency is
significanct for e-Assist system. Flux weakening
control is able to reduce the air gap flux due to the
demagnetizing effect by means of decreasing the
field current and d-axis current in the meantime.
Therefore, this study present the control strategy to
allocate the field current and d-axis current
reasonably for the flux weakening control with
considering losses.
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2.1
Motor analysis
Mechanical structure
In order to achieve the optimal performance, the
geometrical diagram of stator and rotor were
designed as figure 1. The rotor offcenter utilized to
reduce the torque ripple. Hereby, the ripple is
EVS28 International Electric Vehicle Symposium and Exhibition
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9.63% in figure 2 when the maximum torque
generated.
(a)
Figure 3: Mechanical structure diagram
2.2
Back-EMF evaluation
Back-EMF is decided by flux linkage to the
armature current and rotor rotational speed since
equation 1.
E  K e f m
(1)
(b)
Also flux linkage in WRSM is produced by field
current. Thus, the Back-EMF is only related to the
field current at constant speed. Figure 4 shows the
relation between the BEMF and field current.
Fundamental wave of the Back-EMF is given in
figure 5 due to field current variation.
(c)
Figure 1: (a) Design outline of stator (b) Design
outline of rotor (c) Magnetic flux density
Figure 4: Back-emf versus Field current
Figure 2: Torque ripple at the maximum torque
Figure 3 is the mechanical structure of proposed
motor. Unlike the IPMSM, the component 11
and 13 are provided to supply the excitation
current as well as separated dc motor. And
component 9 is additional set into water cooling.
Figure 5: Fundamental wave of the phase Back-EMF
EVS28 International Electric Vehicle Symposium and Exhibition
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Figure 6 Back-EMF comparison between WRSM and
IPMSM
Figure 8: Simulation results
A comparison is present for investigating the
Back-EMF in the identical stator phase resistance
41.6 milliohm and rotor resistance 28.9 ohm in
figure 6.
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Algorithm
One characteristic of WRSM is d-axis inductance
larger than q-axis so that it is able to control in
arbitrary quadrant. The current control is
proposed for operating in the first and second
quadrant t as Figure 7 shown.
Figure 9: Current control strategy
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Experiment
6KW prototype machine was utilized to verify the
aforesaid algorithm. Table 1 gives the specification
of the machine. Current control is implemented
Table 1: A 6kW WRSM Specification
Figure 7: Current vector of proposed strategy
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Simulation
Items
d/q axis inductance
Stator/Rotor resistance
Pole pairs number
Max. field current
DC linkage voltage
EVS28 International Electric Vehicle Symposium and Exhibition
Value
0.42/0.33 [mH]
0.0415/28.944 [Ohm]
3
3 [A]
115 [V]
3
according to the algorithm that illustrated in the
previous section with torque and flux reference
command as figure 9. Machine tested results are
shown in figure 10 versus various field currents.
The maximum efficiency 96% and maximum
regenerative power 5.2 KW were acquired by
proposed algorithm in figure 11, respectively.
and Korea Institute for Advancement of
Technology (KIAT). Meanwhile, it was supported
partially by the research fund from Kookmin
University.
References
[1]
Bon-Ho Bae, Seung-Ki Sul, New Field Weakening
Technique for High Saliency Interior Permanent
Magnet Motor, In Conf. Rec. IEEE-IAS, vol. 2,
pp. 898-905, October 2003.
Authors
Qi Wang, integrated M.S. and Ph.D.
degree, study in Kookmin University.
His current research interests in
wound rotor synchronous machine
drive control system.
Figure 10 Efficiency test in various field current from
3000 rpm to 6000 rpm
Geun-Ho Lee received his B.S. and
M.S. in Electrical Engineering and his
Ph.D. in Automotive Engineering in
1992, 1994 and 2010, respectively,
from the Hanyang University, Seoul,
Korea. From 1994 to 2002, he joined
LG Industrial Research Institute
where he developed inverter system
for elevators. Since 2011, he became
professor for Automotive Engineering
at the Kookmin University. His
current research interests include the
advanced control of electrical
machines, and electric vehicles.
Heon-Hyeong Lee, integrated M.S.
and Ph.D. degree, study in Kookmin
University. His current research
interests in Alternator and EPS
control system
Figure 11: Efficiency and generation power map by
measured data
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Conclusion
This study presented a current control strategy of
WRSM for maximum efficiency control and the
desired currents are able to acquire by means of
offline automatic routine.
Acknowledgments
This research was financially supported by the
“Clean diesel automobile key components
industry promotion program” through the
Ministry of Trade, Industry & Energy (MOTIE)
EVS28 International Electric Vehicle Symposium and Exhibition
Kyu-Sung Park, integrated M.S. and
Ph.D. degree, study in Kookmin
University. His current research
interests in AC motor sensorless drive
system.
Kyu-Sung Park, Ph.D. degree, study
in Kookmin University. His current
research interests in permanent
synchronous machine drive control
system.
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