a literature survey on z-source inverter - vsrd international journals ...

VSRD International Journal of Electrical, Electronics & Communication Engineering, Vol. 2 No. 11 November 2012 / 889 

ISSN No. 2231-3346 (Online), 2319-2232 (Print) © VSRD International Journals : www.vsrdjournals.com 

REVIEW ARTICLE 

A LITERATURE SURVEY ON Z-SOURCE INVERTER 

1Vrushali Suresh Neve, 2 P.H. Zope* and 3 S.R. Suralkar 

1Research Scholar, 2 Professor, 3 Professor &HOD, 1,2,3 Department of Electronics & Tele-Communication Engineering, 

SSBT’s College of Engineering & Technology, Jalgaon, Maharashtra, INDIA. 

*Corresponding Author : phzope@gmail.com 

ABSTRACT 

This paper presents an impedance-source (or impedance-fed) power converter (abbreviated as Z-source converter) (ZSC) and its control 

method for implementing dc-to-ac, ac-to-dc, ac-to-ac, and dc-to-dc power conversion. The Z-source converter employs a unique impedance 

network (or circuit) to couple the converter main circuit to the power source, thus providing unique features that cannot be obtained in the 

traditional voltage-source (or voltage-fed) converter (VSC) and current-source (or current-fed) converter (CSC) where a capacitor and 

inductor are used, respectively. The Z-source converter (ZSC) overcomes the conceptual and theoretical barriers and limitations of the 

traditional voltage-source converter (abbreviated as V-source converter) and current-source converter (abbreviated as I-source converter) 

and provides a novel power conversion concept. The Z-source concept can be applied to all dc-to-ac, ac-to-dc, ac-to-ac, and dc-to-dc power 

conversion. 

Keywords : Voltage Source Inverter, Current Source Inverter, Z-Source Inverter. 

1. INTRODUCTION 

There exist two traditional converters: voltage source (VSI) 

and current source (CSI). Fig.1 shows the traditional 

single-phase voltage-source converter (abbreviated as V- 

source converter) structure. A dc voltage source supported 

by a relatively large capacitor feeds the main converter 

circuit, to a single-phase circuit. The dc voltage source can 

be a battery, fuel-cell stack, diode rectifier, and/or capacitor. 

Four switches are used in the main circuit; each is 

traditionally composed of a power transistor and an antiparallel 

(or freewheeling) diode to provide bidirectional 

current flow and unidirectional voltage blocking capability. 

The V-source converter is widely used. 

 

 

additional dc-dc boost converter is needed to obtain a 

desired ac output. The additional power converter stage 

increases system cost and lowers efficiency. 

The upper and lower devices of each leg cannot be 

gated on simultaneously either by purpose or by EMI 

noise. Otherwise, a shoot-through would occur and 

destroy the devices. The shoot-through problem by 

electromagnetic interference (EMI) noise’s misgatingon 

is a major killer to the converter’s reliability. Dead 

time to block both upper and lower devices has to be 

provided in the V-source converter, which causes 

waveform distortion, etc. 

An output LC filter is needed for providing a sinusoidal 

voltage compared with the current-source inverter, 

which causes additional power loss and control 

complexity. 

Fig. 2 shows the traditional single-phase current-source 

converter (abbreviated as I-source converter) structure. 

Fig. 1 : V-Source Converter 

However, it has the following conceptual and theoretical 

barriers and limitations : 

The ac output voltage is limited below and cannot 

exceed the dc-rail voltage or the dc-rail voltage has to 

be greater than the ac input voltage. Therefore, the V- 

source inverter is a buck (step-down) inverter for dc-toac 

power conversion and the V-source converter is a 

boost (step-up) rectifier (or boost converter) for ac-todc 

power conversion. For applications where over drive 

is desirable and the available dc voltage is limited, an 

Fig. 2 : I-Source Converter 

A dc current source feeds the main converter circuit, to a

Vrushali Suresh Neve, P.H. Zope and S.R. Suralkar VSRDIJEECE, Vol. II (XI), 2012 / 890 

single-phase. The dc current source can be a relatively large 

dc inductor fed by a voltage source such as a battery, fuelcell 

stack, diode rectifier, or thyristor converter. Four 

switches are used in the main circuit; each is traditionally 

composed of a semiconductor switching device with reverse 

block capability such as a gate-turn-off thyristor (GTO) and 

SCR or a power transistor with a series diode to provide 

unidirectional current flow and bidirectional voltage 

blocking. 

However, the I-source converter has the following 

conceptual and theoretical 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 I-source inverter is a boost inverter for 

dc-to-ac power conversion and the I-source converter is 

a buck rectifier (or buck converter) for ac-to-dc power 

conversion. For applications where a wide voltage 

range is desirable, an additional dc–dc buck (or boost) 

converter is needed. The additional power conversion 

stage increases system cost and lowers efficiency. 

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. The open-circuit 

problem by EMI noise’s misgating-off is a major 

concern of the converter’s reliability. Overlap time for 

safe current commutation is needed in the I-source 

converter, which also causes waveform distortion, etc. 

The main switches of the I-source converter have to 

block reverse voltage that requires a series diode to be 

used in combination with high-speed and highperformance 

transistors such as insulated gate bipolar 

transistors (IGBTs). This prevents the direct use of lowcost 

and high-performance IGBT modules and 

intelligent power modules (IPMs). 

In addition, both the V-source converter and the I-source 

converter have the following common problems : 

1. They are either a boost or a buck converter and 

cannot be a buck–boost converter. That is, their obtainable 

output voltage range is limited to either greater or smaller 

than the input voltage. 

2. Their main circuits cannot be interchangeable. In 

other words, neither the V-source converter main circuit can 

be used for the I-source converter, nor vice versa. 

3. They are vulnerable to EMI noise in terms of 

reliability. 

impedance-fed) power converter (abbreviated as Z-source 

converter) and its control method for implementing dc-toac, 

ac-to-dc, ac-to-ac, and dc-to-dc power conversion. Fig.3 

shows the general Z-source converter structure. It employs 

a unique impedance network (or circuit) to couple the 

converter main circuit to the power source, load, or another 

converter, for providing unique features that cannot be 

observed in the traditional Voltage and current source 

converters where a capacitor and inductor are used, 

respectively. The Z-source converter overcomes limitations 

of the traditional voltage source converter and current 

source converter and provides a novel power conversion 

concept. 

Fig. 3 : General Structure of the Z-Source Converter 

Fig. 4 : Z-Source Converter Structure Using the Anti- 

Parallel Combination of Switching Device and Diode 

2. Z-SOURCE CONVERTER 

The Z-source converter (ZSC) is a newly proposed power 

conversion concept that is very promising in the above 

mentioned areas of power conditioning especially in 

alternative energy sources and distributed generation. To 

overcome the problems of the traditional voltage source and 

current source converters, in this an impedance-source (or 

Fig. 5 : Z-Source Converter Structure Using the Series 

Combination of Switching Device and Diode


In Fig.3, a two-port network that consists of a split-inductor 

L1 and L2 and capacitors C1 and C2 and connected in X 

shape is employed to provide an impedance source (Zsource) 

coupling the converter (or inverter) to the dc source, 

load, or another converter. The dc source/or load can be 

either a voltage or a current source/or load. Therefore, the 

dc source can be a battery, diode rectifier, thyristor 

converter, fuel cell, an inductor, a capacitor, or a 

combination of those. Switches used in the converter can be 

a combination of switching devices and diodes such as the 

anti-parallel combination as shown in Fig.4, the series 

combination as shown in Fig.5 As examples, Fig 4 & 5. 

Shows two single-phase Z-source inverter configurations. 

The inductance and capacitance can be provided through a 

split inductor or two separate inductors. The Z-source 

concept can be applied to all dc-to-ac, ac-to-dc, ac-to-ac, 

and dc-to-dc power conversion. 

3. Z-SOURCE INVERTER 

Z-source inverter (ZSI) which is based on Z-source network 

can buck and boost the output AC voltage, which is not 

possible using traditional voltage source or current source 

inverters. 

Also the ZSI has the unique ability to allow the dc-link of 

the inverter to be shorted, which is not possible in the 

traditional voltage source inverters. This improves the 

reliability of the circuit .Actually concept of boosting the 

input voltage is based on the ratio of “shoot-through” time 

to the whole switching period. 

Z-source converter is shown in Fig.6 where an impedance 

network is placed between d.c. link and inverter. Z-source 

inverter (ZSI) provides a greater voltage than the d.c. link 

voltage. It reduces the inrush current & hormonics in the 

current because of two inductors in z source network. It 

forms a second order filter &handles the undesirable voltage 

sags of the d.c. voltage source. 

Fig. 7 : Single Phase Z-Source Inverter 

Fig. 7 shows a topology of the single phase Z-source 

inverter, where the impedance network is placed between 

the power source and the single phase inverter .The 

presence of 2 inductors & 2 capacitors in Z-source network, 

allows both switches of same phase leg ON state 

simultaneously, called as shoot-through state & gives 

boosting capability to the inverter without damaging the 

switching devices. During shoot through state energy is 

transferred From capacitor To inductor & hence Z-source 

inverter( ZSI) gains the voltage boosting capability .Diode is 

required to prevent the discharge of overcharged Capacitor 

through the source. 

4. SWITCHING STATES OF A SINGLE 

PHASE Z-SOURCE INVERTER 

Switching 

Output 

S1 S2 S3 S4 

States 

Voltage 

Active 

States 

Zero 

States 

1 0 0 1 Finite 

0 1 1 0 Voltage 

1 0 1 0 

0 1 0 1 

Zero 

Shoot 

Through 

States 

1 1 S3 S4 

S1 S2 1 1 

1 1 1 1 

Zero 

Fig. 6 : Z-Source Inverter 

As shown in table, a single phase Z-source inverter has five 

possible switching states: two active states (vectors) when 

the dc voltage is connected across the load, two zero states 

(vectors) when the load terminals are shorted through either 

the lower or the upper two switches and one shoot through 

state (vector) when the load terminals are shorted through 

both the upper and the lower switches of any one leg or two 

legs. These switching states and their combinations 

introduce a new PWM method for the Z- Source inverter [2, 

7, 12].


Fig.8 shows the operating states of the single phase Z- 

source inverter in shoot through states that two switches of 

one phase leg or two phase legs are turned on 

simultaneously. 

v i = V c -V L = 2V C - V dc … (4) 

Therefore the average DC-link voltage across the inverter 

bridge over one switching cycle (T) is: 

… (5) 

By applying T 1 = T -T O in Eq.5: 

… (6) 

Where Do is the shoot through duty cycle and Vd, is the 

input voltage source. 

5. SINGLE-PHASE Z-SOURCE INVERTER 

TOPOLOGY 

There are two basic Z-source converter topologies, 

including voltage-fed and current-fed, as shown in Fig.9. 

The Z-source networks are symmetric in these topologies. S 1 

and S 2 are turned on and off in complement. Defining the 

duty ratio of S 1 as D, then we can get the relationship 

between voltage ratio and D of voltage-fed and current-fed 

topologies, respectively: 

Fig. 8 : Operating Modes of a Single Phase Z-Source 

Inverter (A) Shoot through Zero State (B) Non Shoot 

through States 

… (7) 

In Fig.8-a, a diode placed at the input side is reverse biased 

and the capacitors charge the inductors [9] and the voltage 

across the inductors is: 

V L1 = V C1 , V L2 =V C2 … (1) 

With the assumption of symmetric impedance network (C 1 = 

C 2 =C and L 1 =L 2 =L), it can be observed that V L1 = V L2 = V L 

and I L1 = I L2 =I L and the DC-link voltage across the inverter 

bridge during a shoot through interval (To ) is: 

v i = 0 … (2) 

Fig.8-b shows the Z-source inverter in the traditional active 

and null states and due to a symmetric Z-network, inductors 

current (I L1 , I L2 ) and capacitors current (I C1 , I C2 ) are equal. 

The diode at the input side is turned on and the voltage 

across the inductors is: 

V L = V dc - V C … (3) 

The DC-link voltage across the inverter bridge during a nonshoot 

through interval (Ti ) is: 

Fig. 9 : Basic Topologies of Z-Source Converter 

Fig.10 shows the voltage gain versus D of voltage-fed and


current-fed topologies, respectively. For voltage-fed 

topology, it clearly shows that there are two discontinuous 

operation regions. For current-fed topology, we can see that 

the output voltage vary continuously. When D is less than 

0.5, output voltage is in-phase with input voltage. When D 

is greater than 0.5, output voltage is out-of-phase with input 

voltage. This unique feature can be utilized to realize DC- 

AC power conversion, as shown in Fig.11. 

Fig. 11 : Single-Phase Z-Source Inverter Topology 

6. OPERATING PRINCIPLE OF SINGLE- 

PHASE Z-SOURCE INVERTER 

The duty ratio of S 

1 

is D and the coupled inductor of L 

1 

and 

L 

2 

is M. Two states exist in one switching period, and Fig.12 

shows their equivalent circuits. In state 1, switch S 

1 

is turned 

on and S 

2 

is turned off. The time interval in this state is DT, 

where T is the switching period, as shown in Fig. 12 (a). We 

can get 

Fig. 10 : Voltage Gain Versus D of Two Basic Topologies 

Fig.11 (a) shows the basic single-phase Z-source inverter 

topology. v i = v c can be derived easily in steady state from 

Fig.11(a), then we can get the improved topology with input 

and output sharing the same ground, as shown in Fig.11(b). 

The unsymmetrical Z-source network is composed of input 

voltage source v i , capacitor C, and inductors L 

1 

, L 

2 

, where 

L 

1 

and L 

2 

can be coupled inductors with any coupled factor.


In steady state, we get, 

Fig. 12 : Equivalent Circuits in One Switching Period 

Suppose, v 0 = V sin ωt .substituting to (11), we get : 

While A=V/v i 

Substituting (12) to (11), we get : 

i L2 = i o (1- A sin ωt) … (13) 

In state 2, S 

2 

is turned on and S 

1 

is turned off. The time 

interval in this state is (1-D)T, as shown in Fig. 12 (b). We 

can get, 

The voltage stress across the switches is : 

V ds1 = V ds2 =2V i + V … (14) 

The peak current across the switches is : 

Î p1 = Î p2 = Î L1 + Î L2 = Î 0 / D … (15) 

where Î L1, Î L2 , Î 0 are peak values of iL1, iL2, io, 

respectively. 

As can be seen from Fig.12 (b), in the interval (1-D)T, iL1 

charges C, so the Z-source capacitor voltage ripple can be 

expressed as : 

From (8) and (9), we can get the averaged equation 

i L1 can be expressed as : 

By instituting (12) and (17) in (16) ,we get : 

From (18), we can see that are there is the fundamental and 

its double frequency in the Z-source capacitor voltage 

ripple. The input current can be expressed as :


where K =1/k T s =1. 

7. ONE-CYCLE CONTROL STRATEGY 

The realization of the one-cycle controlled single-phase Z- 

source inverter is shown in Fig..13 Fig.14 shows the 

principle waveforms in steady state. 

In steady state, the average voltage across inductor L 1 is 0. 

We get : 

From (22) and (23), we get : 

Therefore : 

Fig. 13 : One-Cycle Controlled Single-Phase Z-Source 

Inverter 

Fig. 14 : Principle Waveforms 

When the clock signal arrives, S1 is turned off and S2 is 

turned on. Then Vds(S1) is integrated from zero. The 

integration value is : 

CSI VSI ZSI 

As inductor is used 

in the d.c link, the 

source impedance 

As capacitor is 

used in the d.c 

link, it acts as a 

As capacitor & 

inductor is used 

in the d.c link, it 

is high. It acts as a low impedance acts as a constant 

constant current voltage source. high impedance 

source. 

A CSI is capable of 

withstanding short 

circuit across any 

two of its output 

terminals. Hence 

momentary short 

circuit on load and 

misfiring of 

switches are 

acceptable. 

Power loss should 

be high because of 

filter. 

Lower efficiency 

because 

of high power loss. 

A VSI is more 

dangerous 

situation as the 

parallel capacitor 

feeds more 

powering to the 

fault. 

Power loss is 

high. 

Efficiency 

should be low 

because of 

power loss high. 

Voltage source. 

In ZSI misfiring 

of the switches 

sometimes are 

also acceptable. 

Power loss should 

be low. 

Higher efficiency 

because of less 

power loss. 

Where k is the integration factor, when the integration value 

reaches Vi-v ref , the integrator resets. S1 is then turned on and 

S2 is turned off. D is determined as : 

The main circuits 

cannot be 

interchangeable. 

This is used in only 

buck or boost 

operation of 

inverter. 

The main circuit 

cannot be 

interchangeable 

here also. 

This is also used 

in only a buck or 

boost operation 

of inverter. 

Here the main 

circuits are 

Interchangeable. 

This is used in 

both buck and 

boost operation of 

inverter. 

The average value of Vds(S1) is :


8. CONCLUSION 

Z-Source Converter is a novel concept which helps to 

implement all dc-to-ac, ac-to-dc, ac-to-ac, and dc-to-dc 

power conversion in a significant low cost system as 

compared to traditional inverter.ZSI can be used in buck and 

boost operation From Study, Z-Source Converter having 

more reliability and Higher Efficiency than traditional 

converters. 

9. REFERENCES 

[1] T. Chandrashekhar , M. Veerachary “Control of Single-Phase 

Z-source Inverter for a Grid Connected System”, 2009 Third 

International Conference on Power Systems, Kharagpur, 

INDIA December 27-29 

[2] S.W.Mohod, P.H.Zope, Modeling & Simulation Of Signal 

Phase Switch-Mode Inverter For Utility Interface ICSCI 

2007. Held At Hyderabad 

[3] S.W.Mohod, P.H.Zope, Modeling And Simulation Of Single 

Phase Switch –Mode Inverter For Utility Interface., National 

IEEE Conference NCDSP 07, Bandra, Mumbai 

[4] M. Shen, F. Z. Peng "Operating modes and characteristics of 

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for a Single Phase Z-Source Inverter", AUPEC 2006, 

Melbourne, Nov 2006. 

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Applications, vol. 42, no. 3, pp. 770-777, May/June 2006. 

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•••

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