ABSTRACT:
In this paper, a high step-up Quasi-Z Source (QZS) DC-DC
converter is proposed. This converter uses a hybrid switched-capacitors switched-inductor
method in order to achieve high voltage gains. The proposed converter have
resolved the voltage gain limitation of the basic QZS DC-DC converter while
keeping its main advantages such as continuous input current and low voltage
stress on capacitors. Compared to the basic converter, the duty cycle is not
limited, and the voltage stress on the diodes and switch isn’t increased. In
addition to these features, the proposed converter has a flexible structure, and
extra stages could be added to it in order to achieve even higher voltage gains
without increasing the voltage stress on devices or limiting the duty cycle.
The operation principle of the converter and related relationships and
waveforms are presented in the paper. Also, a comprehensive comparison between
the proposed and other QZS based DC-DC converters is provided which confirms
the superiority of the proposed converter. Simulations are done in PSCAD/EMTDC
in order to investigate the MPPT capability of the converter. In addition, the
valid performance and practicality of the converter are studied through the
results obtained from the laboratory built prototype.
KEYWORDS:
1.
DC-DC
converter
2.
High
step-up
3.
Impedance
network
4.
Quasi-Z
source
SOFTWARE:
MATLAB/SIMULINK
CONCLUSION:
An improved QZS based DC-DC converter with high step up capability
was proposed. In addition to the QZS network, the proposed converter has used a
combined method of switching-capacitors and switching-inductor. It could
resolve the voltage gain limitation of the basic converter while keeping its
main advantages such as continuous input current and low voltage stress on
capacitors. The maximum duty cycle and voltage stress on the switch and diodes
are remained unchanged. Therefore, they will not affect the voltage gain of the
converter in practice. Extra stages can also be added to the converter to
achieve even higher voltage gains. It was seen after increasing the stages.
Circuit operation principles,
analysis, and necessary relationships were presented. A comparison between the proposed
and other QZS based converters was also provided. Considering the results, the
superiority of the proposed converter to other structures was confirmed. The
simulations were done in PSCAD/EMTDC using a photovoltaic panel input. The results
have confirmed the MPPT capability of the converter.
A 150W prototype of the proposed
converter was also synthesized in the laboratory. The experimental results have
confirmed the theoretical analysis, and, the practicality of the converter and
its proper efficiency have been assured. Considering the approved advantages of
the converter such as continuous input current, high voltage gain, low voltage stress
on elements, and MPPT capability, it could be a suitable choice in a variety of
industrial applications such as photovoltaic systems, fuel cells, PMSG based
wind turbines, and, power systems based on battery banks and super capacitors.
Also, in applications such as uninterruptable power supply (UPS), and LED
lamps, low and varying voltage of the battery and fuel cell should be converted
to the standard DC bus voltage (380-400V), which the proposed converter can be a
suitable choice for them. The point which also should be mentioned is that,
considering the non-isolated structure of the proposed converter, in
applications which an isolation between the input and output side is required,
an isolating transformer could be used in series with the converter.
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