S.Navaneethan et al, International Journal of Computer Science and Mobile Computing, Vol.4 Issue.3, March- 2015, pg.

618-625
Available Online at www.ijcsmc.com

International Journal of Computer Science and Mobile Computing

A Monthly Journal of Computer Science and Information Technology

ISSN 2320–088X

IJCSMC, Vol. 4, Issue. 3, March 2015, pg.618 – 625

RESEARCH ARTICLE

An Effective Method over Z-Source Inverter to

Reduce Voltage Stress through T-Source Inverter
G.Hemaprabha1
Asst.Prof Dept. of EEE
J.Srisaikaviya , S.Navaneethan3, S.Dharani4, P.Ajay5
2

Department of Electrical and Electronics Engineering

Info institute of engineering, Coimbatore, Tamilnadu
2
srisaikavi94@gmail.com, 3 s.navaneethan94@gmail.com
4
dharanisuba11@gmail.com, 5 sendmailstoajay@gmail.com

Abstract- The main objective of this paper is to provide an effective method over traditional inverter technologies for
yielding greater voltage boost and reduced voltage stress across the components. The proposed method utilises high
frequency low leakage inductance transformer accompanied with a capacitor. In this analysis in PWM control methods
we apply maximum boost control across inverter switches for attaining maximum boost voltage. Proposed inverter
network resembles T-shape network hence thereby known as T-source inverter. TSI thus has lesser amount of
components, high voltage gain and hence reduced voltage stress across network. Simulation is done for the proposed
model using MATLAB/Simulink software and hardware results are also verified.
Keywords: TSI, ZSI, shoot through, boost

I. INTRODUCTION
An inverter is an electronic converter which converts dc-ac it is generally applied renewable energy
generation and UPS. Thus inverter with high voltage boost with high efficiency is of great demand. The
traditional inverter topologies include voltage and current fed inverters. In voltage fed inverter topology
a capacitor is kept in parallel with the dc source in this effective buck operation can be obtained but this
topology does not found to be satisfactory for boost operation for which it requires additional networks.
Whereas though current fed inverters provide good voltage boost it produce undesirable
electromagnetic distortion and does not provide buck mode of operation [9].To overcome the main
disadvantage of voltage and current fed inverters Z-source inverter topology was suggested with LC-
lattice network. Though Z-source inverter provides satisfactory operation of buck-boost modes voltage
stress across inverter components is considerably high, thus reducing efficient boosting of voltage
levels. T-source inverter thus employing few reactive components found to be effective in operating in
buck-boost modes with considerable reduction in voltage stress.

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 S.Navaneethan et al, International Journal of Computer Science and Mobile Computing, Vol.4 Issue.3, March- 2015, pg. 618-625

Fig 1.1 T Network

II. Z-SOURCE INVERTER

Fig 1.2 Z-Source inverter circuit

A Z-source inverter consists of LC-lattice network topology for providing voltage buck-boost modes by
implementing shoot through and non-shoot through modes of operation which is not possible in
traditional inverters. The lattice network is composed of two ports with split inductor and capacitor in
X-shape which serves as an impedence source coupling with the inverter.

A. Advantages of ZSI
ZSI founds advantageous over traditional VSI and CSI in following aspects

 It secures the function of increasing and decreasing voltage in single step energy processing.
 It improves power factor and reduces harmonics.
 It provides low cost, reliable buck-boost capabilities.

B. Disadvantages of ZSI
Considerable drawbacks present in Z-source inverter are
 Voltage stress across reactive components of Z-network is more.
 The efficiency of ZSI is quiet less when compared to other traditional inverters.
 Z-source inverter produces discontinuous form of input current and high values of di/dt hence it
requires LC filter at input side.

III. T-SOURCE INVERTER

T-source inverter provides a topology of network alternative to other existing inverter topologies. It
consists of high frequency low leakage inductance transformer accompanied with a capacitor. Hence
has lesser amount of components compared to conventional ZSI. Due to this efficiency appreciably

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 S.Navaneethan et al, International Journal of Computer Science and Mobile Computing, Vol.4 Issue.3, March- 2015, pg. 618-625

increases. By varying the ratio of transformer other than 1:1 facilitates the change in output voltage. It
operates in two modes:

 Shoot through mode.

 Non-shoot through mode.

A. Shoot through mode

This shoot through state prohibited in traditional voltage source inverter. It can be obtained in three
different ways by shoot through via any one phase leg or two phase leg. As diode is reverse biased in
this mode it separates dc link from ac. A desired voltage can be maintained at the output by controlling
the interval of shoot through state. Thus the T –source inverter highly improves the reliability of the
inverter since short circuit across any phase leg is allowed also it do not destroy the switches in the
inverter.

Fig.1.3.Equivalent circuit shoot through mode

B. Non-shoot through mode

In this mode, the inverter operates in one of traditional mode, hence acts as a current source on viewing
from T –source circuit. During this state, the voltage is obtained across load. The diode carries current
difference between the inductor current and input dc current. Here due to coupled inductor same current
exists between these two inductors.

Fig.1.4.Equivalent circuit for non-shoot through mode

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 S.Navaneethan et al, International Journal of Computer Science and Mobile Computing, Vol.4 Issue.3, March- 2015, pg. 618-625

IV. DESIGN OF T-SOURCE INVERTER

During the design of TSI the most challenging is the estimation of values of the reactive components of
the impedance network.. Calculation of the average current of an inductor.
Assumptions made are:
 Drop across diode is negligible.
 For symmetrical t network
 L1=L2; VL1=VL2=VL,
 Total switching period (Tt) = T1+T0
 T1-non shoots through time period (active state)
 T0-shoot through time period (zero state)

For non-shoot through mode for the time period of T1,

Vi = Vdc (2.1)
Vi = Vl1+Vc
Vc = Vi- VL (2.2)
Vl= Vi-Vc

Vout = Vc- Vl2

Vout = Vc- VL
Vout = 2Vc-Vdc
Vi=Vdc (2.3)

In shoot through mode for the time period of T0,

Vc = Vl2 (2.4)
Vc = Vl
Vout = 0 (2.5)

At steady state the average voltage of the inductor for one switching period (TT) is zero.then

Vl= =0 (2.6)

Vc= vdc (2.7)

The average dc link voltage over t source inverter bridge is,

Vdclink=

Vdclink=vdc

Vdc link = Vc (2.8)

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 S.Navaneethan et al, International Journal of Computer Science and Mobile Computing, Vol.4 Issue.3, March- 2015, pg. 618-625

The peak dc link voltage over inverter bridge is

Vdc link peak =VC – VL=2VC-VDC (2.9)

Vdc link peak=VDC = B Vdc (2.10)

B=

B= 1

( )=d0 is shooting through duty ratio

Boost factor depends on shoot through zero time period (T0). the peak dc-link voltage is the equivalent
dc-link voltage of inverter.

Vac=Mi (2.11)

M -modulation index
Peak phase value of output voltage of
inverter is

Vac=MiB (2. 12)

Bb = Mi b = (0 ~ ∞)
Bb - buck boost (gain) factor
The capacitor voltage can expressed as

Vc= Vdc (2.13)

V. PULSE WIDTH MODULATION

PWM signals are used to control the gate pulses fed to inverter circuit for achieving maximum
boost voltage output. There are three control strategies adopted :simple boost control (SBC),
maximum boost control (MBC), constant boost control (CBC).The modulation index also defined
as amplitude modulation ratio (M) which is the main control factor is defined as the ratio of
amplitude of reference wave to the amplitude of carrier wave.
M = Vref / Vcar

VI. MAXIMUM BOOST CONTROL METHOD

Reducing the voltage stress under a desired voltage gain now becomes important to the control of TSI.
MBC maintains the six active states unchanged and turns all zero states into shoot through zero states.
Thus maximum voltage boost is obtained for any given modulation index without distorting the output
waveform. The circuit is in shoot-through state when the triangular wave is either greater than the
maximum curve of the references values or smaller than the minimum of the references. It should
maximize the boost factor for any given modulation index to achieve the maximum voltage gain.
Consequently, we have to make the shoot through duty ratio as large as possible. The shoot through

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 S.Navaneethan et al, International Journal of Computer Science and Mobile Computing, Vol.4 Issue.3, March- 2015, pg. 618-625

duty cycle varies with each cycle.low frequency ripple are introduced in current and voltage waveform
due to presence of inductor and capacitor in the circuit[1].

Fig.1.4.Maximum Boost Control

VII. EXPERIMENTAL RESULT

Simulation model for three phase T-source inverter was designed by using MATLAB/SIMULINK
software.fig.1.5-1.8 shows output voltage, current, operating pulse, phase voltage of T-source inverter
with maximum boost control technique. In this model input voltage of 100V is boosted upto 325V by
shoot through mode of T source inverter.

TABLE I
PARAMETERS AND
VALUES OF T-INVERTER
Parameters Values used in simulation
T-source inverter
DC supply voltage 100V
T-source capacitance
46μF

T-source magnetizing
1.1mH
inductance

T-source leakage inductances

1.5 μH

Transformer Turns Ratio

1:1

Switching frequency 10 kHz

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 S.Navaneethan et al, International Journal of Computer Science and Mobile Computing, Vol.4 Issue.3, March- 2015, pg. 618-625

SIMULATION OUTPUT:

Fig 1.5-simulated output voltage.

Fig 1.6-simulated output current.

Fig 1.7-operating pulse

Fig 1.8-phase voltage

VIII. CONCLUSION
The proceeded concepts are simulated and implemented and results are verified. Use of active snubber
circuit in the network minimises the effect of leakage inductance. By varying modulation index through
maximum boost pwm control maximum voltage boost is obtained. Reduction in number of components
and usage of common voltage source for T-network and inverter reduces the voltage stress and
harmonics in the circuit[2]. These satisfactory results encourage the further researches in implementing
different turns ratio in transformer windings for obtaining greater efficiency.

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 S.Navaneethan et al, International Journal of Computer Science and Mobile Computing, Vol.4 Issue.3, March- 2015, pg. 618-625

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