Step-Up DC/DC Converters with the Tristate
Quasi-Z-Source Network
S. Diwahar, S. Surjith Barnala, N. Vikneswaran & M. Gurunathan
Kalasalingam Institute of Technology, Tamilnadu
E-mail : diwahar.92@gmail.com
Abstract – This paper presents the Step-Up DC/DC
Converters With The Tristate quasi- Z-Source Network. This
paper is based on the step-up dc/dc converter family with a
cascaded quasi-Z-source network. The tri-stage network
could be derived by adding of one diode, one inductor, and
two capacitors to the two quasi-Z-source inverter. It has
advantages of Voltage boost and buck functions in a single
stage, continuous input current and improved reliability.
Theoretical analysis of the tri-stage quasi Z-Source network
in the shoot-through and non-shoot-through operating
modes is described. To further decrease the shoot-through
duty cycle at the same voltage boost factor, the number of
stages of the quasi Z-Source-network could be increased.
impedance network connected between the dc source
input. The Traditional Neutral Point Clamped (NPC)
inverter uses two Z-Source impedance network for
boosting the dc input voltage to a higher value
respectively. The Fig.1 shows the traditional method of
q-ZSI. Although it is not a favorable solution since it
uses two isolated dc sources and a number of passive
elements
which can increase the cost of the project.
Therefore it is not economical because it increases the
cost, size and weight of the inverter. The above
disadvantages are overcome by the following inverter
consisting of a single z-source NPC inverter and a single
dc cascaded inverter that uses only half of the passive
elements and only a non isolated dc source.
Keywords – DC–DC power conversion, power conditioning
units (PCUs), pulse width-modulated power converters,
rectifiers.
II. EXISTING METHOD
I.
INTRODUCTION
Fig.1: Traditional Method
The Three level Z-Source inverter is an inverter
used for the buck boost energy conversion. The three
level Z-Source inverter uses two LC impedance and two
isolated dc source. It is very expensive and it requires a
modulator for balancing the network inductive voltage
boosting. This project presents the design and control of
two three level Z-Source inverters whose output voltage
can be stepped up or down by using only one LC
Fig. 2 : Existing Method
The circuit of the two-stage qZSI during the shootthrough states is shown in Fig.2. This paper is mainly
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International Journal of Advanced Electrical and Electronics Engineering, (IJAEEE)
used on the power conditioning units (PCUs) for
residential power systems. PCUs are used to
interconnect distributed energy sources
to the
residential loads. The distributed energy sources used
here are the low voltage sources such as fuel cells, solar
panels etc. Due to safety and dynamic performance
requirements, the PCU should be realized within the
dc/dc/ac concept. This means that low voltage from the
energy source first passes through the front-end step-up
dc/dc converter. Afterward, the output dc voltage is
inverted in the three-phase inverter and then the ac
voltage is obtained. The front-end step-up dc/dc
converters provides a very high voltage gain. This paper
analyzes the design of the two-stage qZSI, whereas the
design and operation of the converter remain the same
as those with traditional isolated full-bridge converters.
To regulate the varying input voltage, the front-end
qZSI has two different operating modes: shoot-through
and non-shoot through modes.
the two stage q-ZSI network. Therefore the proposed
inverters can operate with the correct Amplitude-time
average and the inductive voltage boosting is produced
all the times. Therefore with the pulse width modulation
scheme the proposed inverter can operate with the
correct amplitude-time and the inductive voltage
boosting is produced at all the instances. The cost of the
inverter is not reduced. Further it doubles the cost
needed for the traditional NPC inverter.
In the non-shoot-through mode, the qZSI performs
only the voltage buck function. This operation mode is
typically used during light-load conditions, when the
output voltage of an fuel cell or a solar panel reaches its
maximum. The inverter is controlled in the same manner
as with the traditional VSI, such that only one switch in
each phase leg conducts. The transistors in the fullbridge configuration are controlled alternately in pairs
such as T1 and T4 or T2 andT3 with 180°-phase-shifted
control signals. In this operating mode, the duty cycle of
inverter switches could never exceed 0.5. When the
input voltage drops below some predefined value, the
qZSI starts to operate in the shoot-through mode. In
order to boost the input voltage during this mode, a
special switching state called the shoot-through state is
implemented in the pulsewidth modulation (PWM)
inverter control.
Fig.3 : Proposed Method
The proposed z-source inverter are controlled with
the ac outputs existing between the three voltage levels
of the +Vdc, 0V, -Vdc using the phase leg switching
states. Alternatively when voltage boost operation is
commanded both inverters must function with an
additional shoot through state inserted. The simplest
method for introducing the shoot through state is turned
on all the switches. The process of turning on of all the
switches from a single phase leg to effect a short circuit
is not the minimal loss method.
This shoot-through state is forbidden in the
traditional network, because it would cause a short
circuit of dc capacitors and destruction of power
switches. The cascaded qZS network makes the shootthrough states possible, effectively protecting the circuit
from damage. Moreover, the shoot through states are
used to boost the magnetic energy stored in the dc-side
inductors L1, L2, L3 and L4 without short circuiting the
dc capacitors C1, . . . , C4. This increase in the magnetic
energy, in turn, provides the boost of the voltage during
the shoot through state.
Therefore the proposed z-source inverter do not
need time delay for the short circuit protection unlike
most traditional inverters and the inverter is expected to
perform the better process.
To reduce volume and cost of z-source network the
low-frequency current ripple should be eliminated and
also greater voltage boost is desired for reducing voltage
stress across switches. The shoot through duty cycle is
kept same to maintain constant boost. The Voltage stress
for simple control, maximum boost and for our proposed
maximum constant boost control are compound. This
can be done by comparing the ratio of voltage stress and
equivalent dc voltage in which the low voltage stress
across devices for proposed method than the other
III. PROPOSED METHOD
The proposed z source inverter consists of three
stage LC network with the cascaded q-ZS inverter
network. The modulation in the network is done by the
Pulse Width Modulation (PWM) scheme. The operation
performed in the three stage q-ZSI network is same as
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International Journal of Advanced Electrical and Electronics Engineering, (IJAEEE)
control methods. Finally this method can be simulated
experimentally by giving input to the parameters such as
L1, L2,C1,C2,. It can be verified that the output voltage is
zero when all four switches are turned on
simultaneously to produce shoot through state. And also
during shoot through period capacitor is charging the
inductor and the inductor current increases during the
shoot-through state with no low frequency ripples in the
inductor current. The proposed method is compared
with other methods to check its effectiveness. Voltage
stress is low in proposed method and the passive
components requirements is minimized. It achieves
maximum voltage boost factor with the continuous
conduction than the traditional operation.
checking the output voltage is same as input voltage
without any harmonic injection. So, by the three stage
qZSI network, the voltage boosting capability is
increased. The voltage stress and current stress are
reduced further. The duty cycle value is reduced from
0.33 to 0.25 respectively. The comparision of the
different stages q-ZSI network is shown in the fig.5.
IV. SIMULATION RESULTS
proposed method of three stage qZSInetwork
The simulation results indicates the pulse
generation for the proposed work which is shown in the
Fig.4. In the Fig the conduction of the thyristors T 1, T2,
T3, T4 of the inverter are shown respectively. First the
thyristors T1 and T2 are conducting with the normal
operating mode. The normal operating mode is also
known as non-shoot through mode. The non shoot
through mode mode takes place during the light load
conditions. At that time the thyristor T 4 is triggered by
the pulse width modulation technique. So that the non
conduction period of the thyristors T 1 and T2 are made
to have the continuous conduction by the triggering of
the thyristor T4 respectively.
existing method of two stage qZSI network
Fig. 5 : Comparison of different methods
V. CONCLUSION
In the existing system the main drawbacks are
greater voltage boost are required, voltage stress and
current stress are maximum across the devices,
clamping circuits are required, the parasitic components
gets reduced the voltage gain. Our proposed method will
overcome the above drawbacks. The boosting capability
will be increased and the voltage stress & current stress
are get reduced. By turning all the zero states in to
shoot through states, the voltage stress is minimised and
the inverter gets maximum boost. It is only suitable for
the applications with fixed or high output frequency and
not for variable and low output frequency since it
requires large dc Inductor when the output frequency is
very low due to the low-frequency current ripple.
VI. REFERENCES
[1]
Fang Zheng Peng,: Z-Source Inverter, IEEE
TRANSACTIONS ON INDUSTRY APPLICATIONS,
VOL. 39, NO. 2, MARCH/APRIL 2003
[2]
Poh Chiang Loh,: Three-Level Z-Source Inverters
Using a Single LC Impedance
Network , , IEEE
TRANSACTIONS ON INDUSTRY APPLICATIONS,
MARCH/APRIL 2007
[3]
Miaosen Shen : Constant Boost Control of the ZSource Inverter to Minimize Current Ripple and
Voltage Stress , IEEE TRANSACTIONS ON
INDUSTRY APPLICATIONS, MARCH/JUNE2006
[4]
Chandana
Jayampathi
Gajanayake:
Extended-Boost
Z-Source
Inverters,
EEE
TRANSACTIONS ON POWER ELECTRONICS,
VOL. 25, NO. 10, OCTOBER 2010.
Fig. 4 : Pulse generation for the proposed work
And then the thyristor T 3 and T4 is conducting in
the shoot through mode. Now the thyristor T 2 is
triggered at that time. So that again the non conduction
period of the thyristors T3 and T4 is to have the
continuous conduction. The simulation is done for
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