Middle-East Journal of Scientific Research 24 (5): 1847-1853, 2016
ISSN 1990-9233
© IDOSI Publications, 2016
DOI: 10.5829/idosi.mejsr.2016.24.05.23308
Enhanced Step-Up Converters for Half Bridge Inverter PV System
1
P. Vinoth Kumar, 2A. Suresh and 3M.R. Rashmi
St.Peter’s University, Chennai, India
Professors, SA Engineering College, Chennai, India
3
Amrita School of Engineering, Bangalore, Chennai, India
1
2
Abstract: In this paper an efficient single phase step up converter is used to boost the voltage obtained from
PV cells. It also provides neutral point terminal to the half bridge inverters. Here, two high steps up converters
which are symmetrical are combined to get an efficient converter with neutral point terminal. Also, the voltage
gain of the converter is enhanced. By using coupled inductor multiplier narrow turn-off period is avoided and
the voltage stress is reduced. Switching losses are reduced because switches act in zero-voltage-switching
condition. The simulation results are presented in this paper.
Key words: Step-up
Converters
Inverters
PV system
INTRODUCTION
With the fast depletion of non-renewable resources,
it is inevitable to adopt renewable energy sources
like solar energy, wind energy to produce electricity.
The added advantage of renewable energy sources is that
they do not cause pollution [1, 2].
In particular, PV systems have been adopted widely
in the society for power generation. The inverter that is
associated with the PV systems has to consume less
power and give high efficiency [3-5]. When the PV system
is used for low power applications, it is desired to avoid
transformers in the design. This reduces cost and weight
of the system [6].
When full bridge inverter is used, it results in
problems like parasitic capacitance and lower efficiency.
There is a need for another solution to rectify these
problems [7, 8].
Many full bridge inverters used so far contribute to
increased conduction losses and have a large number of
switches [9-14]. In this context, half bridge inverters solve
the problem of leakage current by providing a neutral
point terminal [15, 16].
But, the half bridge inverters require twice the
amount of dc bus voltage as that of full bridge inverters
and also a neutral point of the bus. So the main aim is to
design a highly efficient step up dc-dc converters [17].
These converters must not only boost the voltage but
Fig. 1: Proposed system
also give a neutral point terminal. This implementation
is shown in Fig. 1. The existing boost converters have
the disadvantages of high switching losses and narrow
turn off Period [18]. For large voltage conversions,
switched capacitor converters were designed [19-22]. As
a result, voltage stress was decreased [23].
The switched capacitor contributes to conduction
losses and increases the size of the system. The turns
ratio of transformer can be employed in isolated
converters to get good voltage gain [24- 27]. Optimal duty
cycles can also be achieved. From the isolated converters,
the non isolated ones are derived [28-33].
To increase the voltage conversion ratio, coupled
inductors maybe used [34, 35]. New designs have
developed with coupled inductor and switched capacitor
[36].
The proposed design does not deal with the above
discussion. It consists of an improved step up converter
which can create a natural neutral point and enhances the
voltage gain.
Corresponding Author: P. Vinoth Kumar, Reasearch Scholar, St.Peters University, Chennai, India.
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Fig. 2: Block diagram of the system
Fig. 3: Input voltage
Circuit Description and Working: The circuit diagram of
the proposed system is shown in Fig.2. This circuit
consists of inductors, MOSFET switches, regenerative
diodes and switching capacitors. The components are
connected carefully so as to obtain maximum efficiency
and performance.
The PV cells tap the abundantly available solar
energy from the sun and convert it into electrical energy.
The obtained voltage is of a low level which cannot be
converted to DC and directly fed into the grid.
Hence, this DC voltage is boosted to an acceptable
level by the step up converter which has neutral point
terminal. This stepped up DC voltage is given to a half
bridge inverter which converts it into AC. This ac voltage
is fed into the grid.
Thus, a two-step conversion occurs between the PV
panel and the grid to which we feed the voltage.
Simulation Results: The simulation results for the
proposed system are given in this section. It can be seen
that the waveforms resulting in each step have different
magnitude and structure.
The input voltage of 40V is represented by
Fig. 3.
The MOSFET switches are usually driven by the
pulses which are shown in Fig. 4.
The voltage and current waveforms across switch S1
and S2 are shown in Fig. 5 and 6 respectively.
The current and the voltage across the inductors
L1,L2,Lk vary as shown in Fig.7.
Similarly the currents and voltages through the
regenerative diodes Do1,Do2 are shown in Fig.8. and Fig.9.
respectively.
The currents in the diodes Dc1 and Dc2 take the
waveforms as shown in Fig. 10.
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Fig. 4: Driving pulse for MOSFET switches
Fig. 5: Vgs, Ids and Vds across switch S1
Fig. 6: Vgs, Ids and Vds across switch S2
Fig. 7: Vgs and Current through inductor L1,L2,Lk
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Fig. 8: Current through diode Do1,Do2
Fig. 9: Voltage across diode Do1,Do2
Fig. 10: Current through diode Dc1,Dc2
Fig. 11: Current through diode Dr1,Dr2
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Fig. 12: Output current
Fig. 13: Output voltage
Fig. 14: Output power
The currents in the diodes Dr1 and Dr2 take the
waveforms as shown in Fig.11.
A current of nearly 3A and voltage of 400V is
obtained as as the output which take the waveforms as
shown in Fig. 12 and Fig. 13. respectively.
The output power of the system varies as shown in
Fig.14
Fig.15 describes the relation between the input
voltage and the output voltage. It can be inferred that it is
almost a linear relation.
CONCLUSION
Fig. 15: Input voltage vs. Output voltage
The main aim of any system would be to enhance the
performance and reduce losses. The main advantage of
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this system is its efficient operation and an improved
voltage gain. When the voltage stress is reduced
we can ensure better working of the components of
the system. An added advantage is that by providing
neutral point terminal, half bridge inverters can be used
easily.
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