A Novel Indirect Quasi-Z-Source Matrix Converter Applied to Induction Motor Drives

Shuo Liu1, Baoming Ge1,4, Member, IEEE

1School of Electrical Engineering Beijing Jiaotong University

Beijing 100044, China Email: 11117356@bjtu.edu.cn, gebm@msu.edu

Haitham Abu-Rub3, Senior Member, IEEE 3Department of Electrical and Computer Engineering

Texas A&M University at Qatar Doha 23874, Qatar

Email: haitham.abu-rub@qatar.tamu.edu

Xinjian Jiang2

2Department of Electrical and Computer Engineering Tsinghua University

Beijing 100084, China Email: jiangxj@mail.tsinghua.edu.cn

Fang Z. Peng4, Fellow, IEEE 4Department of Electrical and Computer Engineering

Michigan State University East Lansing, MI 48824 USA Email: fzpeng@egr.msu.edu

Abstract—The traditionally matrix converter is a buck AC-

AC power conversion and the maximum voltage gain is limited to 0.866. The paper proposes a new indirect quasi-Z-source matrix converter, to extend the voltage gain for application in the induction motor drives, and then the operation principle and control scheme are clarified. A simulated application in a 4 kW induction motor drive is carried out. Theoretical calculations and feasibility of the proposed topology are verified. The proposed indirect quasi-Z-source matrix converter can boost voltage gain larger than one.

Key words— Induction motor drives, matrix converter, quasi-Z-source inverter.

I. INTRODUCTION

The matrix converter (MC) has been investigated in both academy and industry for over decades. It has many attractive features, such as no dc-link capacitor, four-quadrant operation, adjustable input power factor, and high quality voltage/current waveforms, which not only allows a more compact implementation but also considerably increases the system lifetime due to the absence of the bulky dc-link capacitor compared to the conventional back-to-back converter [1]-[5]. The MC topologies include direct matrix converters (DMCs) and indirect matrix converters (IMCs). The IMCs avoid the commutation problems of the DMCs [5], and are more practical when compared to the DMCs. However, conventional IMCs present the buck conversion characteristic with the voltage gain less than 0.866, which limits its wide applications, especially in adjustable speed drive (ASD) areas. So, how to improve the voltage gain has become a crucial problem.

Several research works on the MC's over-modulation have been carried out to overcome the inherent limitation of the voltage gain. They extended voltage gain at the cost of low frequency harmonics in both the output voltage and input current [6], [7]. A family of Z-source direct matrix converters

was proposed in [8] -[10]. However, they need the complicated commutation, like conventional MCs.

In the paper, a three-phase quasi-Z-source indirect matrix converter (QZSIMC) topology is proposed, which needs one switch, two inductors, and two capacitors. It overcomes the voltage gain limitation of traditional IMC and also exhibits the inherent benefits of IMC. The fundamental operation modes of the proposed converter are explained and the related theoretical equations are derived. In addition, the QZSIMC-based induction motor drive is simulated to demonstrate the performances of proposed QZSIMC. Finally, simulation results verify the high voltage gain and quality performance of the proposed motor drive.

II. TOPOLOGY AND EQUIVALENT CIRCUITS OF THE

PROPOSED QZSIMC

A. Proposed Topology

The QZSIMC topology is shown in Fig. 1. It is a two-stage converter which consists of the rectification stage and the inversion stage. The QZS network is a combination of two inductors L1 and L2 and two capacitors C1 and C2. This combined circuit is connected between the rectification stage and the inversion stage.

au

bu

cu

a

b

c

A

B

C

AC Source

Quasi-Z-source network

Front-end rectifier

Back-end inverter

AC load

M

1L 2L

1C

2C

xS

inu

Cu

Li

LuCi

P

N

PNu

di

Figure 1. Topology of proposed quasi-Z-source indirect matrix converter.

This work was supported by NPRP grant NPRP-EP No. X-033-2-007 (sections II and III) and No. 09-233-2-096 (sections IV and V) from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors.

2440978-1-4799-0336-8/13/$31.00 ©2013 IEEE

au

bu

cu

a

b

c

A

B

C

1L 2L

1C

2C

xS

Cu

Li

LuCi

inu

P

N

PNu

di

(a)

au

bu

cu

a

b

c

A

B

C

1L 2L

1C

2C

xS

Cu

Li

LuCi

inu

P

N

PNu

di

(b)

Figure 2. Equivalent circuits of the QZSIMC. (a) nonshoot-through state; (b) shoot-through state.

B. Equivalent Circuits

The main reason that the quasi-Z-source network is employed to the IMC is to widen the voltage gain by utilizing the boost function [11]-[18].

Fig. 2 shows the equivalent circuits for the shoot-through and nonshoot-through stages. During the nonshoot-through state of Fig. 2 (a), switches Sx are on (Sx=1) for the normal operation. On the other hand, during the nonshoot-through state of Fig. 2 (b), switches Sx are off (Sx=0) and the back-end inverter is short circuit for boost operation.

C. Circuit Analysis

Because of high switching frequency, the quasi-Z-source inverter stage can be considered as a voltage source inverter fed by a constant dc voltage.

During the nonshoot-through state, from Fig. 2 (a), one can get the following voltage and current equations

11 1

CL d

duC i i

dt (1)

22 2

CL d

duC i i

dt (2)

11 1

Lin C

diL u u

dt (3)

22 2

LC

diL u

dt (4)

where iL1, iL2, and id denote the currents of two inductors and the DC-link bus, respectively; uC1, uC2, and uin denote the

voltages of two capacitors, and QZS network input voltage, respectively; C1 and C2 denote the capacitances of capacitors 1 and 2, respectively; L1 and L2 denote the inductances of inductors 1 and 2, respectively.

During the shoot-through state, from Fig. 2(b), we can get the following equations:

11 2

CL

duC i

dt (5)

22 1

CL

duC i

dt (6)

11 2

Lin C

diL u u

dt (7)

22 1

LC

diL u

dt (8)

For one switching cycle Ts, if the interval of shoot-through state is T0, the shoot-through duty ratio is defined as D=T0/Ts. The average voltage of the inductors and the current of the capacitor over one switching period should be zero in a steady state. From (1)-(8), we have

21

(1 ) CC

D uu

D

(9)

2 1 2C in

Du u

D

(10)

1 2L Lin

Pi i

u (11)

where P is the input power of the system.

The output voltage of QZS network is

in

CCPN

uD

uuu

21

121

(12)

The voltage boost factor B is expressed as

Du

uB

in

PN

21

1

(13)

The voltage gain G of the proposed QZSIMC will be calculated by

G Bm (14)

where m=mimo is the modulation index of the indirect matrix converter, mi is the modulation index of the front-end rectifier, and mo is the modulation index of the back-end inverter.

Fig. 3 shows the voltage gain versus the modulation index m. The voltage gain of proposed QZSIMC can be larger than one through choosing the modulation index m and shoot-through ratio D.

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Figure 3. Voltage gain versus modulation index of the proposed QZSIMC.

III. PARAMETER DESIGN

The inductance and capacitance of quasi-Z-source network are designed according to the current ripple and voltage ripple, respectively.

According to the equations

LL

diu L

dt , C

C

dui C

dt ,

from (5)-(8), one can get

2 1 2 11 2 1 2

1 2 1 2

( ), , ,L s L s in C s C s

C C L L

i DT i DT u u DT u DTu u i i

C C L L

(15)

where ΔuC and ΔiL are the peak values of the voltage and current ripples, respectively.

Define

,C C C L L Lu r u i r i ,

where rC is the capacitor voltage ripple ratio and rL is the inductor current ripple ratio.

Using (9)-(12) and (15), we can get

2

1 2 1 22 21 2

(1 2 ) (1 2 ) (1 ), ,

(1 2 )(1 )s s in s

LC in C in

PD D T P D T u D DTC C L L

Pr Dr D u r u

(16)

IV. QZSIMC-BASED INDUCTION MOTOR DRIVE

The proposed QZSIMC is applied to induction motor drive, and the indirect field oriented control is achieved. As shown in Fig. 4, the q-axis current component reference i*

qs of the stator current is the output of speed closed loop through an elaborate PI regulator. The d-axis current component reference i*

ds of the stator current is constant, which is equal to the excitation current of induction motor. The d-axis and q-axis current component closed-loops will ensure the error-free tracking. The shoot-through duty ratio D is used to boost voltage.

V. SIMULATION RESULTS

The QZSIMC based induction motor drive shown in Fig. 4 is simulated to verify the proposed QZSIMC’s steady-state and dynamic performance. The system parameters are shown in Table I.

∫

refr

r *qsI

*dsI

sl

dsIqsI

e e

SVP

WMdq

abc Inverter stage

ua ub uc

M

measures

Speed sensor

dqabc

PI

PI

++PI+

+

+

Quasi-Z-source

converter

Rectifier stage

D

Figure 4. Block diagram of QZSIMC-based induction motor drive.

TABLE I. SYSTEM PARAMETERS. Items Value

Input AC source 380 V / 50 Hz

Inductance L1 and L2 0.44 mH

Capacitance C1 and C2 100 F

Induction motor's rated power 4 kW

Induction motor's rated speed 1430 rpm

Induction motor's rated current 8 A

The motor drive system starts from standstill with no load to reach the desired rotor speed 1500 rpm, then there is a 25 N.m step change of load torque after 1.5 s. From 2 s to 3 s, the desired rotor speed decreases to 900 rpm. Fig. 5 shows the simulation results without the boost operation by setting m=1 and D=0. The 540 V dc-link peak voltage is shown in Fig. 5(d), where the QZSIMC is operating in a traditional IMC (no shoot-through), its buck mode makes the motor drive running below 1500 rpm at the rated torque.

To overcome the voltage gain limitation of the traditional IMC, we use the QZSIMC’s boost mode through setting D=0.1. From (13), the voltage boost factor B will be 1.125. Fig. 6 shows the simulation results for this case. The 604 V output voltage of QZS network is achieved in Fig. 4(d). We find that, the QZS network can boost DC-link voltage, and then the proposed QZSIMC can achieve a voltage gain larger than one, which overcomes the drawback of conventional IMC. The increased voltage pushes the motor rotor speed to reach 1500 rpm at the rated load torque.

VI. CONCLUSION

The paper proposed a new three-phase quasi-Z-source indirect matrix converter, which was applied to the induction motor drive. With the buck-boost voltage transfer feature, the QZSIMC overcomed the inherent limitation of conventional indirect matrix converter. The basic topologies and operation principle were illustrated. The simulation results showed that an extended voltage gain larger than one was achieved by the

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proposed quasi-Z-source indirect matrix converter, also the quality performance validated the proposed induction motor drive and all theoretical analysis.

0 0.5 1 1.5 2 2.5 30

500

1000

1500

2000Speed of IM

T(s)

Spee

d(rp

m)

(a)

0 0.5 1 1.5 2 2.5 3-30

-20

-10

0

10

20

30Torque of IM

T(s)

Te(

N.m

)

(b)

0 0.5 1 1.5 2 2.5 3-50-40-30-20-10

01020304050

Three phase output current

T(s)

Cur

rent

(A)

ABC

(c)

0 0.5 1 1.5 2 2.5 30

200

400

600

800

1000DC-link voltage

T(s)

Vol

tage

(V)

(d)

0.5 0.52 0.54 0.56 0.58 0.6-600

-400

-200

0

200

400

600Stator voltage

T(s)

Vol

tage

(V)

(e)

Figure 5. Simulation results without voltage boost (m=1, D=0). (a) speed of motor drive; (b) electromagnetic torque; (c) three phase output currents; (d) DC-link voltage; (e) output one-phase voltage to stator winding.

0 0.5 1 1.5 2 2.5 30

500

1000

1500

2000Speed of IM

T(s)

Spee

d(rp

m)

(a)

0 0.5 1 1.5 2 2.5 3-30

-20

-10

0

10

20

30Torque of IM

T(s)

Te(

N.m

)

(b)

0 0.5 1 1.5 2 2.5 3-50-40-30-20-10

01020304050

T(s)

Cu

rren

t(A

)

Three phase output current

ABC

(c)

0 0.5 1 1.5 2 2.5 30

200

400

600

800

1000Output voltage of the QZS netwrok

T(s)

Vol

tage

(V)

(d)

0.5 0.52 0.54 0.56 0.58 0.6-800

-600

-400

-200

0

200

400

600

800Stator voltage

T(s)

Vol

tage

(V)

(e)

Figure 6. Simulation results with voltage boost (m=0.9, D=0.1). (a) speed of motor drive; (b) electromagnetic torque; (c) three phase output currents; (d) DC-link voltage; (e) output on-phase voltage to stator winding.

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