AC MODULE ANALYSIS AND IMPLEMENTATION OF TWO …AC MODULE ANALYSIS AND IMPLEMENTATION OF TWO STAGE...

AC MODULE ANALYSIS ANDIMPLEMENTATION OF TWO STAGE

INTERLEAVED FLY BACKINVERTER FOR PHOTOVOLTAIC

APPLICATIONS

A.R. PARVEEN SULTHANA1 and B.PADMANABHAN2

1PG Student1 2Department of EEE,

Sathyabama Institute of Science & TechnologyChennai. [email protected]

2Assistant [email protected]

December 30, 2017

Abstract

The electricity requirements of the world including In-dia are increasing at alarming rate and the power demandhas been running ahead of supply. Solar energy is an im-portant source of renewable energy. The large magnitudeof solar energy available makes it a highly appealing sourceof electricity. A photovoltaic cell (PV) is a device that con-verts light into electric current using the photovoltaic effect.Two Stage Interleaved Fly Back has the advantages such ascompact conformation, simple control loop, electric isola-tion, high step-up ratio, high efficiency, etc., therefore is anattractive solution for photovoltaic ac module applications.In this topology, BCM is more preferred compared to DCMand CCM, because of its higher power level, higher effi-ciency and wider switching frequency bandwidth. However,

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International Journal of Pure and Applied MathematicsVolume 118 No. 16 2018, 1087-1103ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

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the control of BCM is more complicated due to its variableswitching frequency. This also leads to the difficulty to getthe accurate mathematical model between the output cur-rent iout and the reference current .iref , iout has a great in-fluence on BCM which leads to the decrease THD of outputcurrent. Meanwhile the realization of MPPT based on themathematical model for two stages interleaved a fly back-inverter prototype is analysed. The PWM control strategiesare investigated for the interleaved fly back micro inverterconcentrating on the loss analysis under different load con-ditions using PIC controller. The main advantages of theproposed converter are that the transformer size can be re-duced due to the lower magnetizing offset current, all theswitches including synchronous ones can achieve the zero-voltage switching, and it has no cross regulation problems.The operational principle, analysis, and design considera-tions of the proposed converter are presented in this paper.

Key Words : Interleaved fly back converter, PV array,girds inverter, MATLAB / Simulink, PWM pulse and ZVS.

1 Introduction

In recent days, because of energy shortage and environmental con-tamination, the renewable energy is increasingly valued and it hasbeen employed worldwide. A typical renewable energy system hasrenewable energy sources, such as wind power generation, fuel cells,and solar systems, convert sources energy into electrical energy,which generate low output voltage3,4. Because of low output volt-age, this system required high DC/DC convertor which convert lowvoltage into high voltage, that commonly used in many renewableenergy system. Thus high step up conversion is most important inrenewable energy sources system because of its high efficiency withsufficiently high step up conversion.

Among the power converter, boost converters have output dcvoltage greater than its input dc voltage and it shown in Figure 2.It consists of switch S1, a dc inductor L1, a diode D1 and a filtercapacitor. Diode D1 is reverse biased, when switch S1 is turned ONand the output is withdrawn from input. The inductor L1 gets en-ergy from the input supply. Diode D1 is forward biased, when the

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switch is turned OFF and the load draws energy from the inductorL1 through the diode1. At this time, the converter makes the out-put voltage V0 higher than its input voltage Vi by having the sumof the input voltage Vi and the inductor voltage VL1. Operation ofthe converter can be divided into two operating modes dependingon the continuity of the DC inductor current iL1: Continuous Cur-rent Mode (CCM) and Discontinuous Current Mode (DCM). Theinductor current iL1 never fall to zero when converter operates inCCM. In steady state operation, the integral of the inductor VL1

over time period TS must be zero14. The average voltage across theinductor L1 over TS is zero2,5.

The project titled An Optimal Control Method for PhotovoltaicGrid-Tied-Interleaved Fly back Micro inverters to Achieve High Ef-ficiency in Wide Load Range aimed at obtaining the control is car-ried out by Boundary conduction mode (BCM) and discontinuousconduction mode (DCM) control strategies are widely used for thefly back micro inverter16. The BCM and DCM control strategiesare investigated for the interleaved fly back micro inverter con-centrating on the loss analysis under different load conditions17,19.These two control strategies have different impact on the loss dis-tribution and thus the efficiency of the fly back micro inverter. Forthe interleaved fly back micro inverter, the dominant losses withheavy load include the conduction loss of the power MOSFETs anddiodes, and the loss of the transformer; while the dominant losseswith light load include the gate driving loss, the turn-off loss ofthe power MOSFETs and the transformer core loss8,9,10. Based onthe loss analysis, a new hybrid control strategy combing the two-phase DCM and one-phase DCM control is proposed to improvethe efficiency in wide load range by reducing the dominant lossesdepending on the load current.

The objective of the project is to Optimal Control Methodfor Photovoltaic Grid-Tied-Interleaved Fly back Micro inverters toAchieve High Efficiency in Wide Load Range is a Boundary con-duction mode (BCM) and discontinuous conduction mode (DCM)control strategies are widely used for the fly back micro inverter.The BCM and DCM control strategies are investigated for the in-terleaved fly back micro inverter concentrating on the loss analysisunder different load conditions. These two control strategies havedifferent impact on the loss distribution and thus the efficiency of

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the fly back micro inverter. In this project, the BCM and DCMcontrol strategies are investigated of the interleaved fly back microinverter concentrating on the loss analysis under different load con-ditions, respectively12. It is noted that the DCM control strategyachieves higher efficiency over BCM for the application of the in-terleaved fly back micro inverter within the power range of 200W.The advantages of two-phase DCM operation are the current shar-ing and the reduction of the current stress between two interleavedphases so that the conduction loss and turn-off loss of the powerMOSFETs and diodes as well as the copper loss of the transformercan be reduced with higher output power6. On the other hand,the advantage of one-phase DCM operation is the reduction of thetransformer core loss, the driving loss of the power MOSFETs withlower output power. Since the output power is a pulsating powerfollowing a squared sine wave, the idea here is to combine two-phaseDCM modulation and one-phase DCM modulation simultaneouslyaccording to different output power during a half-line period so thatthe dominant losses can be optimized and high efficiency is achievedin wide load range7.

2 Block Diagram of Two Stage Inter-

leaved Fly Back Inverter

Figure 1: Interleaved fly back converter

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Figure 1 shows the interleaved two stage fly converter which isoperated by alternatively switching on the two MOSFETs.

Figure 2: Interleaved fly back converter

Figure 2 shows the Mode1 Power switch S1 TON , magnetizingtransformer T1 conducting. S2 TOFF .

Figure 3: Two stage fly back converter

Figure 3 shows the Mode2 Mode1 Power switch S2 TON , mag-netizing transformer T1 conducting. S1 TOFF .

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Vout = Vpk ∗ (TON/Tper) (1)

Where Vpk= peak amplitude of the secondary pulses.

Vout = (Vin−Vswitch)∗(Cs/Cp)−Vrect (2)

3 Simulation Results for Conventional

and Two stage fly back converter Pro-

posed method Discussion

Simulink model for conventional method single stage fly back con-verter for open loop simulation designed and simulated13,18. Figure4 shows the model of open loop conventional system Figure 12shows the Simulink model of solar panel with proposed circuit di-agram presented. Table 2 shows the parameter used in the designof PWM controller .In the open loop system, the input voltage isfrom 48V. The output is sensed and it is increased to 220V11,15.The processed using a PWM controller. The increasing the pulsewidth applied to the MOSFET of the controlled converter20. Forthis purpose, first, the voltage error signal, which is the differenceof the reference and measured voltages, is determined by Eq. (3)

E = Vr−Vm (2)

Where Vref is reference voltage and Vmeas is the actual mea-sured output voltage.

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Figure 4: Simulink model of conventional circuit

Figure 5: Output Voltage of Battery Conversion System

Above Figure 5 shows the output voltage of the battery conver-sion system with X axis as time & Y axis as voltage.

Figure 6: Switching pulse M1 & VDS

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Above figure 6 shows the switching pulse M1 & Drain to Sourcevoltage (VDS). X axis time & Y axis voltage.

Figure 7: Voltage in the conventional fly back converter

Above Figure 7 shows the voltage in the conventional fly backconverter. X axis as time & Y axis as voltage.

Figure 8: Output voltage of the conventional fly back converter

Above Figure 8 shows the output voltage of the conventional flyback converter with X axis as time & Y axis as voltage.

Figure 9: Output current of the conventional fly back converter

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Above figure 9 shows the output current of the conventional flyback converter with X axis as time & Y axis as current.

Figure 10: Output power of the conventional fly back converter

Above figure 10 shows the output power of the conventional flyback converter with X axis as time & Y axis as Power.

Figure 11: Output THD

Above Figure 11 shows the THD of the solar cell energy con-version system.

Figure 12: Simulink model of proposed circuit

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Figure 13: Solar model of proposed circuit

Figure 14: Output voltage of the solar energy conversion system

Above figure 14 shows the output voltage of the solar energyconversion system with X axis as time & Y axis as voltage.

Figure 15: Switching pulse M1, M2

Above figure 15 shows the switching pulse of MOSFET M1 &M2 with X axis as time & Y axis as amplitude.

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Figure 16: Switching pulse M1, VDS

Above figure 16 shows the switching pulse M1 & Drian to Sourcevoltage (VDS) as the more reduced conduction losses with X axisas time & Y axis as voltage.

Figure 17: Transformer1 primary & secondary voltage

Above figure 17 shows the Transformer 1 primary and secondaryvoltage of the fly back converter with X axis as time & Y axis asvoltage.

Figure 18: Transformer2 primary & secondary voltage

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Above figure 18 shows Transformer 2 primary voltage and sec-ondary voltage of the fly back converter with X axis as time & Yaxis as voltage.

Figure 19: Output voltage of the fly back converter

Above figure 19 shows the output voltage of the fly back con-verter with X axis as time & Y axis as voltage.

Figure 20: Output current of the fly back converter

Above figure 20 shows the output current of the fly back con-verter with X axis as time & Y axis as current.

Figure 21: Output power of the fly back converter

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Above figure 21 shows the output power of the fly back converterwith X axis as time & Y axis as Power.

Figure 22: Output current THD

Above figure 22 shows the output current for total harmonicdistortion.

Table 1: Comparison of Interleaved fly back converterFly backConverter

Vin Vo Io THD

Conventional 48V 100V 2A 16.76%Proposed 48V 220V 52A 7.78%

Table 1 consists of comparison of interleaved fly back converterin terms of total harmonic distortion.

Table 2: Parameters used in the simulation studiesParameters Value

Vs (Input Voltage) 48VVo 220VFs (Switching Frequency) 10KHzL1 100mHC (Capacitance) 80 µFR (Load Resistance) 100Ω

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Table 2 consists of parameter analysis of interleaved fly backconverter for total harmonic distortion.

4 Conclusion

In conventional method voltage ratio is low and high voltage stresswith 16.76% THD but in the proposed method increased voltageratio and reduced voltage stress with 7.78% THD. Also performancecomparison between the conventional and proposed method wasdiscussed in table 1. Comparatively the output voltage ratio alsoincreased in the proposed system. The present work deals withopen loop simulation study and the simulation results closely agreewith theoretical results.

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