Abstract–This the variation of the output current from the

Abstract–This project proposes a design method for
Z-source network based on inductor current. In Z-source inverter, when the
variation of the output current from the Z-source network is large, the
variation of the inductor current and the capacitor voltage increase in the
Z-source network. Therefore, discontinuous current mode (DCM) condition
transiently occurred in the Z-source network inductors. DCM condition affects
the operation of the z-source inverter. Against the problem, this project
proposes a new design method of the Z-source inverter to maintain continuous
current mode (CCM) condition. The proposed method is confirmed by simulation
results and circuit experiments.


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The multiple-input DC–DC converter is useful to
combine several input power sources whose voltage levels or power capacity are
different and to get regulated output voltage for the load. Solar panel is
arranged by a combination of more PV cells. Solar panel direction depends upon
the maximum point of the solar radiation, and the radiation is absorbed.  The power is stored in battery or directly
connected to the dc-dc converter for using the dc load.A multiple-input DC–DC converter is useful to obtain the regulated output
voltage several input power sources such as a solar and fuel cell source.       A basic block diagram shows that solar
energy source is connected to DC-DC Converter transfers energy to the load.


Photovoltaic technology is the one that converts
solar energy directly into electricity, through the use of solar cells or
similar devices. A solar cell constitutes the basic unit of a PV generator
which, in turn, is the main component it. A photovoltaic generator, also known
as a photovoltaic array, is the total system consisting of all PV modules
connected in series or parallel with each other .Solar energy, along with other
renewable energy resources, that does not deplete in source, is reliable, and
environment-friendly. Especially, solar power is arguably the
cleanest, most reliable form of renewable
energy available, and that can be used power home. Solar
owered  photovoltaic(PV) panels convert the sun’s rays into
electricity by exciting electrons in silicon cells using the photons of light
from the sun.


single-phase voltage-source converter (abbreviated as V source converter).The
main converter circuit, is feed by dc voltage source with large capacitor .The
dc voltage source can be a battery, diode rectifier, fuel-cell stack, and/or
capacitor.F2our switches are used in the main circuit; each is composed of a
power transistor and freewheeling diode to provide bidirectional current flow
and unidirectional voltage blocking capability. The V-source converters are
widely used. There are two

Traditional v-  Source Inverter

the traditional
single-phase current-source converter (abbreviated as I-source converter)

Z-source inverter (ZSI) which is based on Z-source
network can be used to 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 short the dc link, 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 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 in the current because of two
inductors in z source network. It forms a second order filter the undesirable
voltage sags of the dc voltage source.

FIG.2.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.


This shoot-through zero state (or vector) is not
present in the traditional VSI, otherwise shoot-through would occur. This extra
zero state (vector) is called the shoot through zero state (or vector). This
shoot-through zero state can be produced in seven different ways:

• shoot-through via any one phase leg

combinations of any two phase legs

all three phase legs

The Z-source network has accomplished the
shoot-through zero state. This shoot-through zero state gives the special
buck-boost feature to the inverter. Figure-6.1 depicts the equivalent circuit
of the ZSI when seen from the dc link . The inverter bridge is similar to a
short circuit when the inverter bridge is in the shoot-through zero state, as
depicted in  whereas the inverter bridge
becomes an equivalent current source as depicted in Figure-6.3 when it is in
one of the six active states . The inverter bridge can also be illustrated by a
current source with zero value (i.e., an open circuit) when it is in one of the
two conventional zero states.

FIG.2 Equivalent Circuit of ZSI when
viewed from dc link

FIG.3 Equivalent Circuit of ZSI in Shoot-through state

FIG.4 Equivalent Circuit of ZSI in Active State

It is supposed that L1 is = L2, and C1 = C2. The
output ac voltage equation of PWM based ZSI

is given by:


Where Vac is maximum sinusoidal inverter output
voltage, B is boost factor, M is the modulation index and Vo is input dc
voltage. The product (B.M) is called inverter gain and is expressed by G.

So, equation (1) can be written as

Vac = GVo/2 
…………..  (2)

Boost factor is decided from the given relation

…. (3)










Hybrid energy system
that combines Photovoltaic (PV) and hydrogen fuel cell energy using z source
inverter is simulated. The output voltage from combined solar energy and  hydrogen fuel cell energy is regulated using
z source inverter. Two different types of loads (ac and dc load) is used. The
simulation is done with help of MATLAB software and simulation results are
obtained. In future the same circuit can be extended for more than two sources.


1         Edwin 
Deepak., “Performance analysis of z source cascaded    h-bridge multilevel inverter based on multi
carrier pwm techniques.”

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 4             Milchilegovo, Dimitrivinnikov, Ryszarad
“Impedence source inverterbbased high power dc-dc converter fuel cell

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“Performance analysis of different control stratagies in z source inverter”

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