Transient Analysis of Z-Source Inverter Fed Three-Phase ...ieejournal.com/Vol_4_No_1/Transient...

International Electrical Engineering Journal (IEEJ) Vol. 4 (2013) No. 1, pp. 856-863 ISSN 2078-2365

856 Transient Analysis of Z-Source Inverter Fed Three-Phase Induction Motor Drive by Using PWM Technique

Transient Analysis of Z-Source Inverter Fed Three-Phase

Induction Motor Drive by Using PWM Technique

Jaswant Singh Dept. of Electrical Engineering,

Shri Ram Group of Colleges (SRGC), Muzaffarnagar (U.P.), India.

Abstract- This paper presents Z-Source inverters which have

recently been proposed as an alternative power conversion concept

for adjustable speed AC drives (ASD). It has both voltages buck and

boost capabilities as they allow inverters to be operated in the shoot

through state. It utilizes an exclusive Z-Source network (LC

component) to dc-link the main inverter circuit to the power source

(rectifier). By controlling the shoot-through duty cycle, the inverter

system using IGBTS, reduces the line harmonics, improves power

factor, increases reliability and extends output voltage range. When

this proposed strategy considers like the inverter as a single unit, it

greatly reduces the complexity and cost when compared with

traditional systems. It has reduced harmonics, low switching stress

power and low common mode noise.

Keywords: Induction Motors (IM), Input Filter, Pulse Width

Modulation (PWM), Shoot- through state, Z-source inverters.

I. INTRODUCTION

In this paper, a functional model of Z-source inverter and PWM

modulated Z-source inverter (PWM VSI) using switching function

based on PWM approach concept is studied and the Simulation of the

developed model is proposed with the help of MATLAB/Simulink.

The Traditional Inverters are voltage source inverter (VSI) and

current source inverter (CSI) which consists of a diode rectifier front

end, dc link and Inverter Bridge. In order to improve power factor,

either an ac inductor or dc inductor is normally used. The dc link

voltage is roughly equal to 1.38 times the line voltage. The voltage

source inverter is a buck converter that produces only an ac voltage,

which is limited by the dc link voltage. Because of this nature, the

voltage source inverter and current source inverter are characterized

by relatively low efficiency because of switching losses and

considerable EMI generation. Inverter presents negligible switching

losses and EMI generation at the line frequency. The voltage source

inverter requires an output RLC filter to provide sinusoidal voltage

compared with current source inverter. The RLC output filters causes

additional power loss and control complexity. The voltage source

converter is widely used.

*Corresponding Author: Jaswant Singh are Asst. Prof. & Head in Dept. of Electrical Engineering, Shri

Ram Group of Colleges (SRGC), Muzaffarnagar (U.P.), India [email protected] ).

The switching function concept is a powerful tool in

understanding and optimizing the performance of the static power

converter/inverters. With the developed functional model, the

simplification of the static power circuits can be achieved so that the

convergence and long run-time problems.

II. Z-SOURCE ASD SYSTEM

Z-Source inverter based induction motor drives provides a low cost

and highly efficient two stage structure for reliable operation. It

consists of voltage source for the supply of rectifier section,

impedance network, which consist of two equal inductors and two

equal capacitors, three phase inverter and three phase induction

motor. The rectification of ac voltage is done by rectifier section to

obtain dc voltage for further supply. The rectifier output dc voltage is

now fed to the impedance network. The network inductors are

connected in series arms and capacitors are connected in diagonal

arms as shown in fig.1. Depending upon the boosting factor

capability of impedance network the rectified dc voltage is buck or

boost upto the voltage level of the inverter section (not exceed to the

dc bus voltage) [7]. This network also act as a second order filter and

it should required less inductance and less capacitance.

This paper addressed an efficient PWM based z-source

inverter approach for the control of adjustable speed drive polyphase

Induction motor. The Z-source inverter advantageously utilizes the

shoot through states to boost the dc bus voltage by gating on both the

upper and lower switches of the same phase leg [6]. Shoot through

mode allows simultaneous conduction of devices in same phase leg.

Therefore, On behalf of boost factor of dc-link, a Z-Source inverter

can boost or buck to the voltage to a desired output voltage that is

greater / lesser than the dc bus voltage[7][12].

mailto:[email protected]



Fig. 1. Main circuit configuration of proposed Z-source inverter

ASD system.

The voltage buck and boost capability cannot be achieved by the

conventional converters, but it is easily achieved by the proposed

model. As shown in fig. (1), the inverter main circuit consists of six

switches. These inverters use a unique impedance network (LC),

coupled between the rectifier and inverter circuit, to provide both

voltage buck and voltage boost properties [17].

The unique feature of the Z-Source inverter is that the

output ac voltage can be any value between zero and infinity

regardless of dc voltage. However, three phase Z-Source Inverter

Bridge has one extra zero state when the load terminals are shorted

through both the upper and lower devices of any one phase leg, any

two phase legs, or all three phase legs. This shoot-through zero State

is forbidden in the traditional voltage source inverter, because it

would cause a shoot-through. The Z-Source network makes the

shoot-through zero state efficiently utilized throughout the operation.

The Z-Source inverter Adjustable Speed Drive (ASD) system has

many ASD applications such as:

Steel mills machines, Paper machines (winder, tension reels,

mill stands)

Cement mills, rubber mills, mixers, crushers

Conveyors

Cranes and elevators cars

Variable Torque applications:

Centrifugal pumps

Centrifugal fans

A. Voltage Source Converter: Barriers and Limitations

The ac output voltage is limited below and cannot exceed

the dc bus voltage or the dc bus voltage has to be greater

than the ac input voltage. Therefore, the voltage source

converter is a boost rectifier for ac to- dc power conversion

and the voltage source inverter is a buck inverter for dc-to-

ac power conversion. For applications where over drive is

desirable and the available dc voltage is limited, an

additional dc-dc boost converter is needed to obtain a

desired ac output. The additional power converter stage

increases system cost and lower the efficiency.

The upper and lower devices of each phase leg cannot be

switched on simultaneously either by purpose or by EMI

noise. Otherwise, a shoot through would occur and destroy

the devices. Dead-time to block both upper and lower

devices has to be provided in the voltage source converter,

which causes waveform distortion, etc.

An output RLC filter is needed for providing a sinusoidal

voltage compared with the current source inverter, which

causes additional power loss and control complexity. A dc

current source feeds the main converter circuit, a three-

phase bridge. The dc current source can be a relatively

large dc inductor fed by a voltage source such as a battery

or diode rectifier. Six switches are used in the main circuit;

each is composed traditionally by a semiconductor

switching device with reverse block capability.

However, the current source converter has the

following conceptual and theoretical barriers and

limitations.

Fig. 2. Voltage Fed Z-Source inverter for ASD.

B. Current Source Converter: Barriers and Limitations

The ac output voltage has to be greater than the original dc

voltage that feeds the dc inductor or the dc voltage

produced is always smaller than the ac input voltage.

Therefore, the current source inverter is a boost inverter for

dc to-ac power conversion and the current source converter

is a buck rectifier for ac-to-dc power conversion. For

applications where a wide voltage range is desirable, an

additional dc-dc buck converter is needed.

At least one of the upper devices and one of the lower

devices have to be gated on and maintained on at any time.

Otherwise, an open circuit of the dc inductor would occur

and destroy the devices. Overlap time for safe current

commutation is needed in the current source converter,

which also causes waveform distortion, etc. In addition,

both the voltage source converter and the current source

converter have the following common problems.



They are either a boost or a buck converter and cannot be a

buck-boost converter. That is, the output voltage range is

limited to either greater or smaller than the input voltage.

Fig. 3. Current Fed Z-Source inverter for ASD.

III. MATHEMATICAL ANALYSIS OF IMPEDANCE NETWORK

The impacts of the phase leg shoot through on the inverter

performance can be analyzed using the equivalent circuit shown in

Fig. 4 and Fig. 5. Assume the inductors (L1 and L2) and capacitors

(C1 and C2) have the same inductance and capacitance values

respectively; the Z-source network becomes symmetrical.

Fig. 4. Equivalent circuit when ZSI in shoot through state.

1 2 1 2

2

0

c c c L L L

d L c c

i

V V V V V V

V V V V

V

(1)

Alternatively, when in non shoot through active or null state current

flows from Z-Source network through the inverter topology to

connect ac load during time interval T1.The inverter side of the Z-

source network can now be represented by an equivalent circuit as

shown in Fig.5. The following equations can be written.

2

L dc c

d dc

i c L c dc

V V V

V V

V V V V V

(2)

Fig. 5. Equivalent circuit when ZSI in non shoot through state.

Averaging the voltage across a Z-source inductor over a switching period (0 to T),

1

1 0( )c dc

TV V

T T

(3)

Using equations (1) and (2) The peak DC-link voltage across the inverter bridge is

0

12

21

i C dc dcV V V VT

T

(4)

.i dcV BV (5)

where,

1 0

. . 1T

B i eT T

(6)

B is a boost factor, T-Switching period The peak ac output phase voltage, For Z- source

. .

2 2

i dc

ac

M V B MVV (7)

In the traditional sources

.

2

dc

ac

M VV (8)

where M is modulation index. The output voltage can be stepped up and down by choosing an appropriate buck – Boost factor

. (it varies from 0 to )BB B M (9) The Buck - Boost factor BB is determined by the modulation index

M and the Boost factor B. The boost factor B can be controlled by

duty cycle of the shoot through zero state over the non-shoot through

states of the PWM inverter. The shoot through zero state does not

affect PWM control of the inverter, because it equivalently produce

the same zero voltage to the load terminal. The available shoot

through period is limited by the zero state periods that are determined

by the modulation index.

IV. MODULATION METHOD



PWM inverters can be of single phase as well as three phase types.

Their principle of operation remains similar and hence in this paper

the emphasis has been put on the more general, 3-phase type PWM

inverter. These inverters are capable of producing ac voltages of

variable magnitude as well as variable frequency. The PWM inverters

are very commonly used in adjustable speed ac motor drive loads

where one needs to feed the motor with variable voltage, variable

frequency supply. For wide variation in drive speed, the frequency of

the applied ac voltage needs to be varied over a wide range. The

applied voltage also needs to vary almost linearly with the frequency.

Carrier-based PWM methods are preferred in implementing

modulators for inverters as they are simple and easy to realize in

shown in fig. 6 & 7 To date, there are three types of carrier-based

modulation schemes proposed to modulate single-stage Z-source

inverters [4], [5], [16].

In simple boost modulation method, the shoot-through period is fully

inserted within the traditional null period, and this is achieved simply

by comparing a constant reference value with a carrier signal. With

the second method, the total null period is occupied by shoot-through

period and is known as maximum boost controlling. Although this

method does not increase the total number of switching‟s per half

cycle, it is found to be producing poor dynamic performance under

transient conditions [17], [19]. The modulation method proposed in

[15], has shoot-through period carefully inserted between the state

changes from active to active and active to null. This minimizes the

number of switching‟s per half carrier cycle and achieves improved

spectral characteristics. In this topology, two inverters are connected

to a single dc source through a common Z-source impedance

network. These techniques are commonly used for the control of ac

induction, Brushless Direct Current (BLDC) and Switched

Reluctance (SR) motors. As a result, PWM converter powered motor

drives offer better efficiency and higher performance compared to

fixed frequency motor drives [2].

Fig. 6. PWM Pulse Generation Circuit

Fig. 7. Generation of switching signals with interleaved carrier-based

PWM.

Hence, modulation schemes may need to be modified to suit the

proposed topology. There are two possibilities in deriving the

modulation signals. The first and obvious method is to modulate the

two inverters from a common carrier signal with careful insertion of

shoot-through time with simple boost or minimum switching [4], [15]

methods proposed for a single Z-source inverter. This pulse is used to

switch ON or OFF the power switches. The width of the pulse or duty

cycle can be varied by varying the frequency of the reference wave.

Since the Z-source inverter bridge can boost the dc capacitor (C1 and

C2) voltage to any value that is above the average dc value of the

rectifier, a desired output voltage is always obtainable regardless of

the line voltage. Here inverter bridge switching is provided by pulse

width modulation generator. In order to show clearly the output

voltage obtains from inverter an RLC filter is placed between the

Inverter Bridge and induction motor. Simulation parameters for z-

source are given as follows:

L1=L2= (100e-9) H

C1=C2= (1000e-6) F

V. SIMULATION RESULTS AND DISCUSSION

Fig. 8 shows the main circuit configuration of the z-source fed pwm

induction motor drive, similar to that of the traditional ASD system.

The z-source ASD system‟s main circuit consists of three parts: a

diode rectifier, dc link circuit and inverter bridge.



Fig.8. Simulink Model for Z-source fed PWM - IM Drive.

To confirm the operating principle of the new ASD system,

simulations have been carried out on simulink modeling. In order to

show clearly the output voltage obtained from the inverter, an output

RLC filter is placed in between the inverter bridge and the motor.

Different cases are considered for showing the parameter variation in

the value of load.

Case 1: full load, (Tfl = 11.9N-m)

Case 2: under load condition, (Tul = 8 N-m)

Case 3: Free acceleration condition, (Tfa =0 N-m)

Fig. 9. Input Voltage waveform.

Case-1 Response of Induction motor for full load (Tfl = 11.9N-m)

Fig.10 shows the waveforms of dc-link voltage and current of Z-

source fed pwm induction motor drive. Here dc-link voltage is

boosted to 309 V due to z-source. The dc link voltage is roughly

equal to 1.38 times the line voltage (220 V). This shows that the Z-

source inverter is a can only produce an ac voltage which is not

limited by the dc link voltage. Fig.11, 18 shows inverter voltage

before output filter and load voltage after output filter circuit. After

output filter load voltage is Vrms=220 V and before output filter is

Vrms=220 V and Vpeakrms =307.8 V Transients in stator and rotor

currents are there for short span of time that is it settles quickly as

shown in fig 15, 18.

The starting current is high but within 1.16 second, it

reaches to steady state value. Steady state value of stator current

is19.06 A. Steady state value of rotor current is 17.09 A. The result

for the speed estimation are shown in figure 17. It can be observed

that speed reaches at steady state value that is 1718 rpm with in 1.09

second when motor is subjected to constant load 11.9N-m. So when

the motor is fed by Z-source inverter then its speed increases and

setling time decreases .And it is due to voltage after inverter circuit

which boosted to 218V by Z-source inverter. Electromagnetic torque

waveform is shown in fig. 18.

Fig. 10. Waveforms of dc –link voltage of Z –Source.

Fig.11. Inverter output voltage before filter is Vpeak rms =307.00 V.

Fig.12. Inverter output voltage after filter is Vrms=220 V.

Fig.13. Inverter Load voltage after output filter Vpeak rms=304.5 V

Fig. 14. Inverter Load voltage after output filter is Vrms = 220 V.



Fig. 15. Rotor current/phase ir under full load condition ir=19.06A.

Fig. 16. Stator current/phase is under full load condition is =17.09A.

Fig. 17. Rotor Speed Nr under full load condition ns=1714, ts=0.89.

Fig. 18. Electromagnetic Torque Te under full load condition.

Case-2) Response of Induction motor for under load

condition (Tunder load = 8 N-m)

The result for the speed estimation are shown in figure.19-22. It can

be observed that speed reaches at steady state value that is 1745 rpm

with in 0.714 second when motor is subjected to constant load 8 N-m.

So when the motor is fed by z-source inverter then its speed increases

and setling time decreases.

Also the waveform for Rotor speed (rpm), input voltage,

per phase rotor current, per phase stator current and also the

waveform of electomagnetic torque is shown in fig. 19-22.

Fig. 19. Rotor current/phase ir for under load condition.

Fig. 20. Stator Current per phase is for under load condition.

Fig. 21. Rotor Speed in rpm (Nr) for under load condition.

Fig. 22. Electromagnetic torque Tem for under load condition.

Case-3) Response of Induction motor at No load condition

(Tnl =0 N-m)

The result for the speed estimation are shown in fig. 23 - 26. It can be

observed that speed reaches at steady state value that is 1799.4 rpm

with in 0.736 second when motor is subjected to constant load 0 N-

m.So when the motor is fed by z-source inverter then its speed

increases and setling time decreases.

Also the waveform for Rotor speed (rpm), input voltage,

per phase rotor current, per phase stator current and also the

waveform of electomagnetic torque is shown in fig. 23 - 26.



Fig. 23. Rotor current ir at No load condition.

Fig. 24. Stator current/phase is at No load condition.

Fig. 25. Rotor speed in rpm Nr at No load condition.

Fig. 26. Electromagnetic torque Tem at No load condition.

VI. CONCLUSIONS

In this paper, Induction motor with Z-source inverter are proposed

and simulated in SIMULINK/MATLAB. This paper presents a new

PWM adjustable speed drive system based on the Z-source inverter

topology. The performance of three phase induction motor is

analyzed by using this technique, Simulation results are analyzed by

the output waveforms in term of induction motor outputs

(performance parameters).

A Pulse Width modulation technique is used for generating

a desired value of pulses by using an appropriate value of switching

frequencies. Performance of 3-phase Induction motor is investigated

for the different load conditions and their comparison is also

presented in this work.

PWM allows the operation of inverter in over modulation

region. This proposed strategy considers the inverter as a single unit

and greatly reduces the complexity and cost when compared with

traditional systems. It has reduced harmonics, low switching stress

power and low common mode noise.

Simulation has been performed for 3 HP, 220 V, 60 Hz,

1725 rpm, induction motor with PWM z-source inverter and the

results are show that to verify these new features. By comparison we

conclude that z-source fed pwm induction motor drive is more

efficient over Traditional variable speed drive system. Because of

inverter output voltage is more boost up than that of Traditional

variable speed drive system.

VII. REFERENCES

[1] Amitava Das, S.Chowdhury, S.P.Chowdhury, Prof. A. Domijan

„„Performance Analysis of Z – source Inverter Based ASD System with

Reduced Harmonics‟‟ IEEE Trans. Ind. Appl., pp. 1–7, 2008.

[2] Poh Chiang Loh, Feng Gao, Pee-Chin Tan, and Frede Blaabjerg

„„Three-Level AC–DC–AC Z-Source Converter Using Reduced

Passive Component Count‟‟ IEEE, Transactions On Power Electronics

VOL. 24, NO. 7, JULY 2009.

[3] Kuo-Kai Shyu and Hsin-Jang Shieh „„Variable Structure Current

Control for Induction Motor Drive By Space Voltage Vector PWM‟‟

IEEE Trans. on Indu. Electronics, vol. 42, no. 6, pp.572-578,

DECEMBER 1995.

[4] Poh Chiang Loh , Feng Gao and Frede Blaabjerg „„Topological and

Modulation Design of Three-Level Z-Source Inverters‟‟ IEEE

Transactions On Power Electronics, VOL. 23, NO. 5, SEPTEMBER

2008.

[5] D. G. Holmes and B. P. Mcgrath, “Opportunities for harmonic

cancellation with carrier-based PWM for a two-level and multilevel

cascaded inverters,” IEEE Trans. Ind. Appl., vol. 37, no. 2, pp. 574–

582, Mar./Apr. 2001.

[6] Fang Zheng Peng, Alan Joseph, JinWang, Miaosen Shen, Lihua Chen,

Zhiguo Pan, Yi Huan,“Z-Source Inverter for Motor Drives” IEEE

transactions on power electronics , vol. 20, no. 4, july2005.

[7] M. Shen, J.Wang, A. Joseph, F. Z. Peng, L. M. Tolbert, and D. J.

Adams, “Maximum constant boost control of the Z-source inverter,”

presented at the IEEE Industry Applications Soc. Annu. Meeting,

2004.

[8] M. H. Rashid, “Power Electronics, Circuits Devices and Applications”,

Prentice-Hall International Editions, 1992. N. Mohan, T. M. Undeland,

and W. P. Robbins, “Power Electronics‟‟Converters, Applications, and

Design”, John Wiley and Sons, 1989.

[9] S. Thangaprakash, Dr. A. Krishnan, ‘’Z-source Inverter Fed Induction

Motor Drives – a Space Vector Pulse Width Modulation Based

Approach‟‟ Journal of Applied Sciences Research, 5(5): 579-584,

2009.

[10] F. Z. Peng, “Z-source inverter,” IEEE Trans. Ind. Applicat., vol. 39,

no.2, pp.504–510, Mar./Apr. 2003.



[11] E. P.Wiechmann, P. D. Ziogas, and V. R. Stefanovic, “Generalized

functional model for three phase PWM inverter/rectifier converters,” in

Conf. Rrec. IEEE-IAS Annu. Meeting, 1985, pp. 984–993.

[12] S. R. Bowes, “New sinusoidal pulse width modulated inverter,” Proc.

Inst. Elect. Eng., vol. 122, pp. 1279–1285, 1975.

[13] J. Holtz, W. Lotzkat, and A. Khambadkone, “On continuous control of

PWM inverters in the over modulation range including the six-step

mode,” in Proc. IEEE IECON’92, 1992, pp. 307–312.

[14] Poh Chiang Loh, D. Mahinda Vilathgamuwa, Chandana Jayampathi

Gajanayake, Yih Rong Lim, and Chern Wern Teo, „„Transient

Modeling and Analysis of Pulse-Width Modulated Z-Source Inverter‟‟

IEEE Transactions On Power Electronics, VOL. 22, NO. 2, pp. 498-

507, MARCH 2007.

[15] W. Leonhard, “Control of electrical drives”, 2nd Ed, Springer, 1996.

[16] Prof. Krishna Vasudevan, Prof. G. Sridhara Rao, Prof. P. Sasidhara

Rao,Electrical Machines II, National Programme on Technology

Enhanced Learning. W. Leonhard, “Control of electrical drives”, 2nd

Ed, Springer, 1996.

[17] Jin Li1, Jinjun Liu1 and Liu Zeng1,„„Comparison of Z-Source Inverter

and Traditional Two-Stage Boost-Buck Inverter in Grid-tied

Renewable Energy Generation‟‟ IEEE Transactions On Power

Electronics,VOL. , NO. , pp. 1493- 1497, dec.2009.

[18] Yu Tang, Shaojun Xie, Chaohua Zhang, and Zegang Xu,„„Improved Z-

Source Inverter With Reduced Z-Source Capacitor Voltage Stress and

Soft-Start Capability‟‟ IEEE , Transactions On Power Electronics

,VOL. 24, NO. 2, FEBRUARY 2009.

[19] Poh Chiang Loh, Feng Gao, Frede Blaabjerg, Shi Yun Charmaine

Feng, and Kong Ngai Jamies Soon,„„Pulsewidth-Modulated Z-Source

Neutral-Point-Clamped Inverter‟‟ IEEE Transactions On Industry

Applications, VOL.43,NO.5, pp. 1295- 1308,

SEPTEMBER/OCTOBER 2007.

[20] Seyed Mohammad Dehghan, Mustafa Mohamadian, Ali Yazdian, and

Farhad Ashrafzadeh,„„A Dual-Input–Dual-Output Z-Source Inverter‟‟

IEEE Transactions On Power Electronics, VOL. 25, NO. 2, pp. 360-

368, FEBRUARY 2010.

[21] Fang Zheng Peng, Miaosen Shen, and Zhaoming Qian,„„Maximum

Boost Control of the Z-Source Inverter‟‟ IEEE Transactions On Power

Electronics, VOL. 20, NO. 4, pp. 833- 838, JULY 2005.

BIBLIOGRAPHIES

Jaswant singh was born in Firozabad, (U.P),

India in 1987. He received the B.Tech.

degree in Electrical Engineering in 2009

from RGEC, Meerut, India, and M. Tech. in

Electrical engineering (Power electronics &

drive) from the Kamla Nehru Institute of

Technology (KNIT), Sultanpur, (U.P.), 2011,

India. In 2011, he joined the Department of

Electrical & Electronics Engineering, P.K. Institute of Technology &

Management, (PKITM), Mathura, U.P., India, as an Asst. Prof. &

Head in 2011. He is currently an Asst. Professor & Head in

Department of electrical engineering from Shri Ram Group of

Colleges (SRGC), Muzaffarnagar (U.P.), India, where he has been

since August‟2012. He has authored or coauthored 20 publications on

power electronics, control and simulation of electrical machines and

drives. His areas of interest in research are power electronics &

drives and power quality problems.

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