push pull converter based bidirectional inverter for … · the push-pull converter is designed...

ISBN: 97-8-93-81195-82-6 Proceedings of NJCIET 2015

Canara Engineering College, Mangalore NJCIET-2015 512

Push Pull Converter based Bidirectional Inverter for Residential Photovoltaic

Power System

Kiran B Soudia, Nagesh Prabhu

b

aM.Tech Scholar, Department of Mechanical Engineering, NMAMIT, Nitte, Udupi-574 110, India

Email: [email protected] bProfessor & HOD, Department of Electrical Engineering, NMAMIT, Nitte, Udupi-574 110, India

Email: [email protected]

Abstract. Photovoltaic (PV) residential power system is an important application of renewable energy source. The residential

power system works on the principle that the power delivered by solar panel has to be converted from dc to ac for the utility

purpose, in order to arrive with the efficient conversion the soft-switching push-pull converters are used. These have only two

primary devices with common ground to supply and results in straight forward and reduced gating requirement. Soft-switching is

maintaining the secondary modulation and its load independent, during wide variation of input voltage and power transfer

capacity is suitable for PV applications. In this paper, a dual stage dc/ac inverter is designed that is composed of high step-up

push-pull converter and full-bridge inverter. The converter analysis and performance obtained using SIMULINK.

Keywords: Push Pull, Photovoltaic Power System, SIMULINK.

1 INTRODUCTION

The technology development of renewable energy sources such as photovoltaic (PV), fuel cell, wind, etc., are gaining more and

more attention Amongst all the renewable energy sources, PV source plays a key role in energy portfolio of the world because it

is clean and reliable. It is also predicted to make one of the major contributions in electricity generation source by 2040 [1, 2].

In the past, the cost of PV modules was expensive (4.4~7.9 USD per Watt in 1992 [3]) but a downward tendency is now

observed due to the mass production of PV panels. Cost reduction for the power electronics converters becomes important to

make the PV generation more attractive. Therefore, the focus should be placed on new, innovative and cost effective solutions,

which results in a high diversity within the power converters and system configurations [4].

Solar radiant energy is the most usable and available renewable energy source on the earth. Photovoltaic (PV) is a method of

generating electrical energy by converting solar radiation in to electricity using semiconductors which exhibit photovoltaic effect.

The photovoltaic enabling power systems for residential applications have been rapid and significant growing around the world.

However, main drawback is the output voltage of PV panel is low. Thus, connecting the PV panels in series is the conventional

solution. The output power of the PV panel would drop because of the partial shading and module mismatch. The parallel

configuration of the PV panel is more efficient than series connected configuration to fulfil the safety requirements in residential

applications. The PV output voltage is relatively low in case of parallel connected configuration therefore, converters with high

step-up ratio and high efficiency are required to boost the PV Voltage to higher level.

This paper, discusses the implementation of a high-efficiency converter particularly for the solar PV residential power system.

The push-pull converter is designed with a lower voltage rating of the switching devices and a high DC voltage conversion ratio.

The periodic steady-state operation of the converter is analysed.

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mailto:[email protected]



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the no n-co

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2 SOFT SWITCHING PUSH PULL CONVERTER [5]

A dual-stage dc/ac inverter as shown in Fig.2.1. Is a proposed high step-up push-pull converter and standard full-bridge inverter.

Voltage doubler selected to reduce number of the switches and the transformer turns ratio. The secondary modulation technique

is clamps the voltage across the primary side devices and eliminates the necessity for snubber. Switching losses are reduced

significantly by the soft switching technique.

Fig. 2.1 Inverter with high step-up push-pull dc/dc converter

3 OPERATION OF THE CONVERTER

Steady-state operation and analysis of high step-up converter have been explained.

To simplify the analysis, the following assumptions are made:

1. Boost inductor L is large enough to maintain constant current through it.

2. All the components are ideal.

3. Series inductances Llk1 and Llk2 is represented as Llk-T.

4. Magnetizing inductance of the transformer is infinitely large.

The steady-state operating waveforms are shown in fig. 3.1.The primary switches S1 and S2 are operated with identical gating

signals phase shifted with each other by 1800

with an overlap and the overlap varies with duty cycle and that should be kept above 55%.

Steady-state operation of the converter during different intervals is explained using equivalent circuits.

In interval 1(see fig 3.2; t0 ˂ t ˂ t1): primary side switch S2 and antiparallel body diode D3 of the secondary side switch are conducting. Power is transferred the load through HF tran mer. ducti eco

voltage VD nducting primary device S1 i t vo

blocking output

The values ugh various components ar , 0, , ltage across the switch S1: oltage across the switch S4:



Fig. 3.1 Steady state operating waveforms of the converter

Fig. 3.2 Equivalent circuit during time interval of t0 ˂ t ˂ t1

Interval 2(see fig 3.3; t1 ˂ t ˂ t2): At t1=t2, primary switch S1 is turned-on the corresponding snubber capacitor C1 discharges in

a very short period of time. At the end of this interval. S1 is fully conducting and C1 is completely discharged.

Fig.3.3 Equivalent circuit during time interval of t1 ˂ t ˂ t2



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Interval 3(see fig 3.4; t2 ˂ t ˂ t3): Now primary switches are conducting. Rectifier output voltage appears across series ind uctors

Llk1 and Llk2, diverting/transferring the current thro switch S2 to S1. It causes current through previously conducting device

S2 to reduce linearly. It also results nd zero current which helps reducing associated turn-on loss.

The currents through various comp a

. (3.1) . _

. (3.2) .

.

. ( 3.3) .

W Llk L e t the body diode D3 conducting. Therefore, S3 can be gated on for Z - t m s naturally. Current through all primary devices reaches Iin/2. F

d 0.


Interval 4 (see Fig.3.5; t3 ˂ t ˂ t4): Secondary device S3 is turned-on with ZVS. Currents through all the switching devices

continue increasing dec N he e slope i . At the end of this interval, the primary device S2 commutates naturall ro obtaining ZCS. The full current, i.e., input current is taken over by other S

Final values are:


Interval 5 (see Fig.3.6; t4 ˂ t ˂ t5 ): The leakage inductance current Ilk1 increases further with the same slope and antiparallel

body diode D2 starts conducting causing extended zero voltage to appear across commutated switch S2 to ensure ZCS turn-off.

Now, the secondary device S3 is turned-OFF. At the end of this interval, current through switch S1 reaches its peak value. This



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⁄ .

interval should be very short to limit the peak current h the transformer and switch reducing the current stress and kVA

ratings.

The currents through operating

. (3.4) . _

. (3.5) .

. . (3.6) . _

Fig. 3.6: Equivalent circuit during time interval of t4 ˂ t ˂ t5

Interval 6 (see Fig.3.7; t5 ˂ t ˂ t6): During this interval, secondary switch S3 is turned-OFF. Antiparallel body diode of switch

S4 takes over the current immediately. Therefore, the voltage across the transformer primary reverses polarity. The current

through the switch S1 and body diodes D2 also smart decrea .

Current through the operatin b

, − .

. (3.7)

, −

. . (3.8)

. , .

− . . (3.9)

At the end of t D2 r o mmutated naturally. Current through S1 reaches Iin.

Final values: , 0 and




⁄n short pe

during

ugh S1

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Interval 7(see fig.3.8; t6 ˂ t ˂ t7): Snubber capacitor C2 charges to V riod of time. Switch S2 is in forward blocking

mode now.

Fig. 3.8: Equivalent circuit me interval of t6 ˂ t ˂ t7

Interval 8(see fig.3.9; t7 ˂ t ˂ t8): In this interval, currents thro nd transformer are constant at input current I in. Current

through antiparallel body diode of the secondary switch D4 is at


4 SIMULATION RESULTS

Simulat ined based o alues 41V to 22V and delivering . The pr and S2 the , and for the S3 and S4 the value of , . 5Ω, the series

inductors by 11µ H an boost inductor value L=31µ H,input in 4.7mF,output

capacitors 220µ F, the filter inductor LF=5.5mH, filter capacitor CF=0.47µ F. the transformer turns ratio

n=1.84 and duty ratio d=0.6 frequency of the converter is 100 kHZ, frequency of the inverter is 20 kHZ and the output

waveform of the inverter is 50 HZ,R value is 200 Ω.

The push pull converter which is used to increase the input voltage has been designed using simulink as shown in fig.4.1. Fig. 4.2 shows the subsystem model of the converter which contains simpower module blocks.



Fig.4.1 Simulink model for push pull converter

Fig.4.2 Subsystem model of the converter

The output voltage obtained is shown in Fig 4.3. The steady state output voltage of the converter where the output remains

practically constant.



The output obtained from the converter is DC voltage required to convert it AC voltage using the inverter block as shown in

fig.4.4. The inverter output is shown in Fig 4.5. It is observed that, the frequency of converter output is about 50 Hz. Fig 4.6

shows the steady state output current of

satisfactorily.

the inverter. The inverter is tested for variation in load and found to work

Fig.4.4 Simulink model of the inverter

Fig.4.5 Steady state output voltage of the inverter



5 CONCLUSION

In this paper, simulation of the push-pull converter based bidirectional inverter for residential photovoltaic power system has

been verified. It explains how variable solar energy can be constantly accessed through push pull converter, by monitoring

converter output voltage constant.

REFERENCES

1. E. Figueres, G. Garcera, J. Sandia, F. Gonzalez-Espin, and J. C. Rubio, “Sensitivity Study of the dynamics of three-phase

photovoltaic inverters with an LCL grid filter,” vol. 56, no. 3, pp. 706–717, Mar. 2009 IEEE.

2. Q. Li and P. Wolfs, “A review of the single phase photovoltaic module integrated Converter topologies with three different dc link

configurations,” vol. 23, no. 3, pp. 1320–1333, May 2008 IEEE.

3. Trends in Photovoltaic Applications. Survey Report of Selected IEA Countries between 1992 and 2002. International Energy Agency

Photovoltaic Power Systems, IEA PVPS T1-12:2003.

4. S. B. Kjaer, J. K. Pedersen, and F. Blaabjerg “A Review of Single-Phase GridConnected Inverters for Photovoltaic Modules,” vol. 41,

no. 5, pp. 1292-1306, Sept/Oct. 2005 IEEE.

5. Pan Xuewei,Akshay Kumar Rathore” Current-Fed Soft-Switching Push-Pull-Front-End Converter-Based Bidirectional Inverter for Residential Photovoltaic Power System,”vol.29,no.11,November 2014 IEEE.

push pull converter based bidirectional inverter for … · the push-pull converter is designed...

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