06-05-2014, 12:37 PM
Experimental Investigation of In-wheel Switched Reluctance Motor Driving System for Future Electric Vehicles
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Abstract
This paper presents an experimental direct
driving system with in-wheel switched reluctance motor
(SRM) for electrical vehicle (EV). The integrated EV direct
driving system includes three main parts: the SRM model,
driving circuit and control unit. The proposed 8/6 SRM is a
novel motor with high performance; the specified external
rotor type fits the requirement of in-wheel EV for saving
space. The driving module consists of four independent
drivers, is controlled by the micro-controller, DSP. The
detailed hardware installment is presented to realize the EV
direct driving system, with the block diagram to show the
design of the driving system. Control flow of the specified
system is introduced to describe the control procedure;
various control methods are proposed and studied to verify
the performance of SRM and the driving system. Speed
control and constant torque/constant power control are
implemented with PI control and hysteresis loop control, to
test the speed response and reliability of the direct driving
system. An experimental direct driving system is developed;
the experimental results are obtained to verify the
performances of the EV driving system.
INTRODUCTION
Electrical vehicle (EV), comparing to the traditional
vehicle which is driven by internal combustion
engine(ICE), applies an electrical machines as its prime
mover and has many advantages: zero-emissions, high
efficiency, independence from fossil fuel, and quiet and
smooth operation[1][2]. Hence, electrical machines, along
with the power electronics technologies, play an important
role in the development of EV and provide a propulsion
system with high performance and flexibility, especially
for direct driving systems without gearbox.
The switched reluctance motor (SRM) is a novel electrical
machine with high torque at low speed, making it a good
candidate for direct driving purpose. Its torque is produced
by the tendency of its moveable part to move to a position
where the inductance of the excited winding is maximized
[3]. Besides, the SRM has a simple and firm construction
with no windings and permanent magnets in the stators
and rotors. Since the geometrical simplicity of SRM, it has
a lower cost of manufacturing and maintenance than other
types of electrical machine, while the reliability and
robustness appear to be improved. Furthermore, the
driving power converter of SRM has an independent
circuit for each phase, which provides the great advantages
of inherent fault tolerance and the potential of high
reliability.
Power converter
As shown in figure 3, there are four independent inverters
in the power converter module, to drive four phases of the
specified 8/6 SRM, respectively. Here, the winding of
phase A is connected with two terminals, A1, A2, and so
on. Eight IGBTs are used as the switches; the related RC
snubber circuit is added to improve the performance of the
inverter with decreasing di/dt.
During the conducting period of phase A, Q1 and Q2 are
switched on, the current flows from Q1 to Q2 through the
winding of phase A; when a chopping is needed to
decrease the phase current, Q1 is turned off while Q2
keeps on, the current flows through Q2 and D1. Q1 and
Q2 are both switched off when phase A is turned off, the
current flows through D1 and D2 and decreases to zero.
CONCLUSION
This paper presents a direct driving system of EV with the
switched reluctance motor. The developed SRM with
exterior rotor is applied to save space and provide high
reliability and flexibility in motion control. DSP is used to
obtain a reliable and high performance motion control
with high switching frequency of converters. An
experimental system is installed to verify the performance
of the direct driving EV system. Speed control and
constant torque/constant power control are done to
illustrate the performance of the developed SRM and the
speed response of the driving system. From the
experimental results, the driving system can track the
referenced speed rapidly and has a small overshoot.
Besides, the torque/power characteristics of the driving
system meet the requirement of the design, proving that
the developed direct driving EV system is reliable for the
industry application. Furthermore, torque ripple
minimization will be studied to improve the performance
of instantaneous torque of the SRM, hence to improve the
speed response and loading effect to EV.