Application of Random Space Vector Pulse Width

Modulation in Electric Vehicle

Guoqiang Chen

School of Mechanical and Power Engineering, Henan Polytechnic University, Jiaozuo,

454000, China

jz97cgq@163.com

Abstract. Aiming at the electromagnetic radiation and noise problem resulting

from the electric drive system, the application of the random space vector PWM

(SVPWM) strategy is proposed to be used in the electric vehicle (EV). The

random SVPWM strategy is introduced firstly. Furthermore, the closed-loop

control system is analyzed based on the vector control method using the random

SVPWM technology. Finally, the proposed application is verified through an

example. The paper provides a new method and idea in weakening and reducing

the electromagnetic radiation in the EV.

Keywords: Electric vehicle, random space vector PWM, electromagnetic

radiation, harmonic reduction

1 Introduction

The air pollution, PM2.5 for example, is a serious problem in the world, which does

harm to human health [1, 2]. The internal combustion engine vehicle is one main

source. The electric vehicle (EV) has been regarded as one efficient measure to solve

the problem. The motor and the inverter are the key components of the EV. The

permanent magnet synchronous motor (PMSM) has been widely utilized in the EV.

The inverter converts the direct current (DC) electric energy from the battery to the

alternative current (AC) electric energy, and the two-level three-phase inverter has

been widely used because of its simple structure [3]. The electromagnetic radiation

and noise in the EV resulting from the high voltage subsystems is more serious than

the traditional vehicle [4-6]. Therefore to suppress the electromagnetic radiation and

noise is most important. The inevitable undesirable harmonic of the space vector

pulse width modulation (SVPWM) strategy causes the problems of electromagnetic

radiation and noise. The large amplitudes of the cluster harmonics (that makes the

case more serious) can be evidently suppressed using the random SVPWM strategy.

Therefore, the random SVPWM strategy has attracted plenty of study [7-9].

Therefore, the application of the random SVPWM strategy is proposed to be used in

the EV. The random strategy is introduced firstly. Furthermore, the closed-loop

control system is analyzed based on the PMSM vector control method using the

random SVPWM technology. Finally, the proposed application is verified through an

example.

Advanced Science and Technology Letters Vol.143 (AST 2017), pp.89-93

http://dx.doi.org/10.14257/astl.2017.143.18

ISSN: 2287-1233 ASTL Copyright © 2017 SERSC

2 Random SVPWM Strategy

The topology of the inverter and the voltage vector are shown in Fig. 1a) and 1b),

respectively [9, 10]. An arbitrary command voltage vector can be generated by two

adjacent active vectors, and the corresponding control signal waveforms for the upper

arms in the six sextants are shown in Fig. 1b) marked with the notations A, B and C

for the commonly used 7-segment SVPWM pattern.

DC

2

U

A

BC

1T

2T

3T

4T

5T

6T

1D

2D

3D

4D

5D

6D

+

-

+

-

O

P

N

DC

2

U

1(100)U

2 (110)U3(010)U

4 (011)U

5 (001)U6 (101)U

0 (000)U

7 (111)U 1 1TU

2 2T Uα

β

s sTU

A

B

C

A

B

C

A

B

C

A

B

C

A

B

C

A

B

C

1

2

3

45

6

a) The topology of the inverter b) Basic space vectors and the 7-

segment SVPWM pattern

Fig. 1. The inverter topology and the voltage vector

The three random SVPWM schemes includes (1) the random switching frequency

SVPWM (RSFSVPWM) with that the switching frequency or the switching period is

randomized in an interval, (2) the random zero-vector distribution SVPWM

(RZDSVPWM) with that the zero vector duration time distribution ratio between the

two zero vectors is controlled by a random variable, and (3) the random pulse position

SVPWM (RPPSVPWM) with that the pulse positions of the three phases are

controlled by three independent variables.

3 Application of Random SVPWM in EV

The Vector Control (VC, also called field-oriented control (FOC)) and Direct torque

control (DTC) are two main methods used in variable frequency drives to control the

three-phase AC electric motors. The VC and DTC have their advantages and

disadvantages and have been used in all kinds of fields. The significant advantages of

the VC well satisfies the EV application that is required to generate full torque at zero

speed, fast acceleration and deceleration performance, and so on. The closed-loop

control system using the random SVPWM in the EV is shown in Fig.2.

The control system includes the following modules. (1) The phase currents Ai and

Bi are measured using two current sensors, and the phase current Ci is A B( )i i .

Advanced Science and Technology Letters Vol.143 (AST 2017)

90 Copyright © 2017 SERSC

(2)The currents αi and βi are gotten from the three phase currents

Ai ,Bi and

Ci

through Clarke transformation. (3) The rotator position angle of the motor is

measured using an encoder or a rotary transformer. (4) The currents di and qi are

gotten from the currents αi and βi through Park transformation. (5) The actual speed

of the motor is measured using the rotary transformer or computed using the

differential method from the rotator position angle . (6) The control strategy is

selected based on the DC link voltage, command voltage, and so on. (7)The command *

di and *

qi are computed based on the selected control strategy. (8)The command

voltage du and qu are computed using the current controllers, for example PI

controllers. (9) The currents αu and βu are gotten from the command voltages

du

and qu through inverse Park transformation. (10) The 6 control pulse signals are

generated using the random SVPWM strategy.

PI Random

SVPWMInverter

Speed

computation

Encoder/rotary

transformer

PI

n

qi

*

qi*

di

αi

βiΑi

qu DCU

αu

.

.

PMSM

i

.

abc

dq

dq

βudu

di

+

+

Control

strategy

BatteryIntention

interpretation

of the Driver

Fig. 2. The closed-loop control system using the random SVPWM in the EV

4 Example and Performance Analysis

A random SVPWM strategy simulation model is built based on the control system

described in Fig.2. The DC link voltage is 100V. The fundamental frequency of the

implicit modulation waveform is 30Hz. The switching frequency is 5000Hz. The

random zero-vector distribution factor obeys the uniform distribution on the interval

[0,1] for the RZDSVPWM scheme. The three independent variables obey the uniform

distribution on the interval [0,1] for the RPPSVPWM scheme. The simulation results

of the amplitude peak values of the cluster harmonics around the switching frequency

and the double frequency are shown in Fig. 3 for the traditional deterministic 7-

Advanced Science and Technology Letters Vol.143 (AST 2017)

Copyright © 2017 SERSC 91

segment SVPWM strategy, RZDSVPWM and RPPSVPWM schemes. The results are

gotten based on the FFT (Fast Fourier Transformation) of the sampled line-line

voltage data. From the figure, it can be found that the random strategy can

significantly suppress the cluster harmonic amplitude. The following conclusion can

be drawn. Firstly, the deterministic SVPWM strategy and RZDSVPWM strategy

present the maximum amplitude peak values around the double frequency while the

smaller values around the switching frequency if the modulation index is less than 1.

The symmetry of the three-phase switching signals shown in Fig.1b) contributes to

the above phenomenon. Secondly, the RZDSVPWM scheme presents excellent

performance on suppressing the harmonic amplitude peak values around the double

frequency while does little around the switching frequency. The line-line voltage is

symmetrical in the half switching period to some extent, while the random zero-vector

distribution ratio weakens the symmetry. Finally, the RPPSVPWM scheme has more

excellent performance than the RZDSVPWM scheme on suppressing the amplitude

peak values around the double frequency, which results from that the random pulse

position in the RPPSVPWM scheme destroys the symmetry of the pulse voltage

waveforms.

Har

monic

am

pli

tude(

%, of

fundam

enta

l)

Modulation index

Har

mo

nic

am

pli

tud

e(%

, o

f fu

nd

amen

tal)

Modulation index

a) Around the switching frequency b) Around the double frequency

Fig. 3. Amplitude peak values of the cluster harmonic

5 Conclusion

The random SVPWM strategy is proposed to be used in the electric drive system of

the EV. The application has several advantages. Firstly, the proposed method has

significant performance on suppressing the harmonic amplitude peak values. In

addition, the random variable can be realized through the pseudo-random number

generated using the computation formulas. The pseudo-random number array can also

be generated in advance and stored in the read-only memory of the microcontroller

unit. Finally, only the control program should be updated while no change in the

control hardware of the EV is required for some random SVPWM schemes, so the

Advanced Science and Technology Letters Vol.143 (AST 2017)

92 Copyright © 2017 SERSC

algorithm is highly convenient and feasible. However, the universal theoretical

expression for the performance is extremely complicated. This task is our future

study.

Acknowledgments. This work is supported by National Science Foundation of China

(No. U1304525). The author would like to thank the anonymous reviewers for their

valuable work.

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