A Novel Indirect Quasi-Z-Source Matrix Converter Applied to Induction Motor Drives Shuo Liu1, Baoming Ge1,4, Member, IEEE
Xinjian Jiang2
1
2
School of Electrical Engineering Beijing Jiaotong University Beijing 100044, China Email:
[email protected],
[email protected]
Department of Electrical and Computer Engineering Tsinghua University Beijing 100084, China Email:
[email protected]
Haitham Abu-Rub3, Senior Member, IEEE 3
Fang Z. Peng4, Fellow, IEEE 4
Department of Electrical and Computer Engineering Texas A&M University at Qatar Doha 23874, Qatar Email:
[email protected]
Abstract—The traditionally matrix converter is a buck ACAC 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, quasiZ-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.
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.
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 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.
978-1-4799-0336-8/13/$31.00 ©2013 IEEE
Department of Electrical and Computer Engineering Michigan State University East Lansing, MI 48824 USA Email:
[email protected]
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Front-end rectifier
AC Source ua
Sx
L2
Back-end id inverter
AC load
P A
b
uc i C
L1
a
ub
uC
Quasi-Z-source network C2
uin
C1
uPN
c uL
B
M
C
N
iL
Figure 1. Topology of proposed quasi-Z-source indirect matrix converter.
C2 ua
a b
uc uC
Sx
id
L2
P A
ub
i C
L1
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.
uin
uPN
C1
c uL
During the shoot-through state, from Fig. 2(b), we can get the following equations:
B C
N
iL
C1
duC1 iL 2 dt
(5)
C2
duC 2 iL1 dt
(6)
diL1 uin uC 2 dt
(7)
diL 2 uC1 dt
(8)
(a)
C2 ua
a
b
uc uC
Sx
id
L2
L1
P A
ub
i C
L1 uin
C1
uPN
uL
B C
c
L2
N
iL
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
(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.
uC1
(1 D)uC 2 D
(9)
D uin 1 2D
(10)
uC 2
iL1 iL 2
P uin
(11)
where P is the input power of the system. The output voltage of QZS network is
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.
u PN uC1 uC 2
1 uin 1 2D
(12)
The voltage boost factor B is expressed as
During the nonshoot-through state, from Fig. 2 (a), one can get the following voltage and current equations
B
u PN 1 uin 1 2 D
(13)
du C1 C1 iL1 id dt
(1)
C2
duC 2 iL 2 id dt
(2)
G Bm
L1
diL1 uin uC1 dt
(3)
diL 2 uC 2 dt
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.
(4)
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 shootthrough ratio D.
L2
where iL1, iL2, and id denote the currents of two inductors and the DC-link bus, respectively; uC1, uC2, and uin denote the
The voltage gain G of the proposed QZSIMC will be calculated by
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(14)
ua
ub
uc
Rectifier stage
r + ref
+
PI
I
Figure 3. Voltage gain versus modulation index of the proposed QZSIMC.
III.
Items
du diL , iC C C , dt dt
from (5)-(8), one can get iL 2 DTs i DT (u u ) DTs u DT , uC 2 L1 s , iL1 in C 2 , iL 2 C1 s (15) C1 C2 L1 L2
where ΔuC and ΔiL are the peak values of the voltage and current ripples, respectively. Define uC rC uC , iL rL iL ,
where rC is the capacitor voltage ripple ratio and rL is the inductor current ripple ratio. Using (9)-(12) and (15), we can get PD(1 2 D)Ts P(1 2 D)Ts u 2 (1 D ) DTs (16) , C2 , L1 L2 in 2 2 PrL (1 2 D) rC1 (1 D)uin rC 2 uin
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.
dq abc
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.
Inverter stage
M Speed sensor
Figure 4. Block diagram of QZSIMC-based induction motor drive.
According to the equations
C1
I ds
+ e ∫ e +
The inductance and capacitance of quasi-Z-source network are designed according to the current ripple and voltage ripple, respectively.
uC1
I qs
dq abc
PI
sl
PARAMETER DESIGN
uL L
* qs
PI
Quasi-Zsource converter
measures
r
I ds* +
SVPWM
D
TABLE I. SYSTEM PARAMETERS. 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
8A
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 shootthrough), 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.
Speed(rpm)
Speed(rpm)
Speed of IM
2000
Speed of IM
2000
1500
1500 1000 500 0 0
1000
0.5
1
1.5 T(s)
500 0 0
0.5
1
1.5 T(s)
2
2.5
Te(N.m)
Te(N.m)
10
-30 0
-10
0.5
1
1.5 T(s)
(b) 0.5
1
1.5 T(s)
2
2.5
Three phase output current
3
Three phase output current Current(A)
Current(A)
(b) A B C
0.5
1
1.5 T(s)
2
2.5
50 40 30 20 10 0 -10 -20 -30 -40 -50 0
A B C
0.5
1
1.5 T(s)
2
2.5
3
2.5
3
(c)
3
(c)
Output voltage of the QZS netwrok
1000
DC-link voltage
1000
Voltage(V)
800
800 Voltage(V)
3
0 -10
-20
600 400
600 400 200
200
0 0 0.5
1
1.5 T(s)
2
2.5
0.5
1
1.5 T(s)
3
2
(d)
(d) Stator voltage
600
Stator voltage
800 600 400 Voltage(V)
400 Voltage(V)
2.5
10
-20
0
200 0
200 0 -200 -400
-200
-600
-400 -600 0.5
2
20
20
0 0
3
Torque of IM
30
3
Torque of IM
30
50 40 30 20 10 0 -10 -20 -30 -40 -50 0
2.5
(a)
(a)
-30 0
2
0.52
0.54
T(s)
0.56
0.58
-800 0.5
0.6
(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.
0.52
0.54
T(s)
0.56
0.58
0.6
(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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