PERFORMANCE ANALYSIS OF SEVEN LEVEL INVERTER WITH SOFT SWITCHING CONVERTER FOR PHOTOVOLTAIC SYSTEM

50 PERFORMANCE ANALYSIS OF SEVEN LEVEL INVERTER WITH SOFT SWITCHING CONVERTER FOR PHOTOVOLTAIC SYSTEM M.Vidhya 1, Dr.P.Radika 2, Dr.J.Baskaran 3 1 PG Scholar, Dept.of EEE, Adhiparasakthi Engineering College, Melmaruvathur, Tamilnadu, India 2 Professor, Dept.of EEE, Adhiparasakthi Engineering College, Melmaruvathur, Tamilnadu, India 3 HOD, Dept. of EEE, Adhiparasakthi Engineering College, Melmaruvathur, Tamilnadu, India ABSTRACT This paper analyse the performance of Seven Level Inverter which is configured by means of capacitor selection circuit and an H- bridge inverter. Multicarrier Sinusoidal Phase Disposition Pulse Width Modulation (MCSPDPWM) and Variable Frequency Inverted Sinusoidal PWM technique (VFISPWM) are employed for analysing the Total Harmonic Distortion (THD) of the Seven Level output. The capacitor selection circuit converts the output of the Soft Switching Interleaved Boost Converter and solar source into three level direct current (DC) voltage and an H- bridge inverter further converts three level dc voltage to seven level alternating current (AC) voltage. The performance parameters like output voltage and efficiency of two different Soft Switching Interleaved Boost Converters are compared and analysed with the conventional Interleaved Boost Converter. Keywords- Soft Switching Interleaved BoostConverter,Efficiency,Multilevel Inverter, Pulse Width Modulation technique, Total Harmonic Distortion (THD) I. INTRODUCTION Electric power is the most commonly used type of energy. The use of fossil fuels results in the global problem of greenhouse emissions. Moreover the cost of fossil fuel keeps increasing as the supplies of fossil fuels are depleted in the future. Thus solar energy is becoming more important since it produces less pollution. The power conversion interface is important because it converts the dc power generated by the solar cell array into ac power and feeds the utility. An inverter is necessary in the power conversion interface to convert the direct current (DC) into alternating current (AC).Since the output voltage from the solar cell array is not sufficient enough to be given as input to the inverter circuit, a soft switching interleaved boost converter is used. The converter boost the solar cell output so that it can match with the dc bus voltage. Here soft switching interleaving boost converter has been discussed with two different topologies and compared with conventional interleaved boost converter to obtain high voltage gain and efficiency. Multicarrier Sinusoidal PWM technique and Variable Frequency Inverted Sinusoidal PWM technique are employed to analyse the Total Harmonic Distortion of seven level output waveform.seven level inverter with only six power electronic switches was proposed [4]. Hence switching losses are reduced. Two dc dc converters are used to step the output voltage of solar array which leads to complexity of the circuit. Transformer based converter are used which reduces the power efficiency.one H- bridge inverter and two diodeembedded bidirectional switches was proposed [8] to produce seven level. The number of diodes are increased which leads to complex circuit.however three capacitors are used to produce the voltage levels.hence balancing the voltages across three capacitors is more complex. A five level diode clamped multilevel inverter was proposed [3]. A separate dc voltage balancing circuit was equipped to maintain and balance the capacitor voltage. Coupled inductor is also used in the balancing circuit and the amplitude of flux will be reduced by means of the voltage balancing circuit. An interleaved boost converter with a capacitor for battery charger applications was proposed [13]. The capacitor is used for soft switching purpose to reduce the voltage stress of the converter switches and also to improve the efficiency. An interleaved boost converter with zero - voltage transition was proposed [14]. The inductor is used for the soft switching phenomenon to reduce the voltage stress and also to improve the conversion efficiency. Seven level inverter topology with ten power electronic switches and three capacitors was proposed [6].Balancing of capacitor voltage becomes complex and also switching loss increases due to more number of switches. II. PROPOSED METHODOLOGY This paper proposes a seven level inverter which is fed by a solar input source. The input from the solar is stepped up by means of soft switching interleaved boost converter. This paper compares operation of conventional interleaved boost converter with two different topologies. Topology 1 demonstrates theoperation of interleaved boost converter with soft

51 switching inductor and topology 2 deals with the operation of interleaved boost converter with soft switching capacitor. Multicarrier Sinusoidal Phase Disposition PWM and Variable Frequency Inverted Sinusoidal PWM techniques are used for the generation of gate pulses for the inverter switches and the THD of the seven level output voltage are analysed. The circuit diagram of conventional interleaved boost converter is shown in Fig.1 converter. The seven level inverter consists of a capacitor selection circuit and full bridge inverter connected in cascade. The solar input is given to the capacitor C 1 and output from the converter is given to the capacitor C 2. The capacitor selection circuit converts the input dc voltage into three level dc voltage and inverter further converts the three level dc voltage into seven level ac output voltage. The circuit diagram of proposed seven level inverter is shown in Fig. 4 Fig. 1 Circuit Diagram of Conventional Interleaved Boost Converter Topology 1: (Soft switched inductor) The circuit diagram of topology 1 shows the two shunted boost conversion units and a soft switching inductor is used to improve the efficiency and also to increase the output voltage. Fig. 2 shows the circuit diagram of topology 1 Fig. 2 Circuit Diagram of Topology 1 Topology 2: (Soft switched capacitor) The circuit diagram of topology 2 shows the two shunted boost converter units and a soft switching capacitor to improve the efficiency and also to increase the output voltage. The circuit diagram of topology 2 is shown in Fig. 3 Fig.4 Circuit Diagram of Seven Level Inverter with Topology 2 The output voltage of the seven level inverter has the following voltage levels: V dc, V dc /3, 2Vdc/3, 0,- V dc /3,-2V dc /3,-V dc.the different modes of operation for obtaining the seven level output voltage was discussed below. The operation of seven level inverter in positive half cycle is divided into four different modes. Mode 1: In mode 1 operation both the switches S S1 and S S2 of the capacitor selection circuit are turned OFF.S 1 and S 4 switches of the full bridge power converter are turned ON and C 1 is discharged through diode D 1 to obtain a voltage level of V dc/3.the operation of mode 1 is shown in Fig.5 Mode 2: In mode 2 operation, S S2 of the capacitor selection circuit and S 1 and S 4 of the full bridge power converter is ON and C 2 is discharged through the diode D 2 toobtain a voltage level of 2V dc/3.the equivalent circuit of mode 2 is shown in Fig.5 Mode 3: In mode 3 operation, in the capacitor selection circuit S S1 is ON.S 1 and S 4 of the full bridge power converter is turned ON to obtain V dc output voltage level. The mode 3 operation is shown in Fig. 5(c) Mode 4: In mode 4 operation, all the switches are turned OFF to get a zero output voltage level and its operation is shown in Fig. 5(d) Fig. 3 Circuit Diagram of Topology 2 Proposed Seven Level Inverter with Topology 2 (Capacitor) The proposed seven level is fed by means of solar input through a soft switching interleaving boost

52 with different topologies and seven level inverter with topology 2 has been simulated in MATLAB Simulink model. Fig.7shows the Simulink model of conventional interleaved boost converter. (c) (d) Fig. 5 Operation of different modes in positive half cycle Mode 1 mode 2 (c) mode 3 (d) mode 4 Mode 5: In mode 5 operation, the switches S2 and S3 of the full bridge power converter are turned ON and capacitor C1 is discharged through the diode D1to obtain a voltage level of Vdc/3.The equivalent circuit of mode 5 operation is shown in Fig. 6 Mode 6: In mode 6 operation, switches S S2, S 2 and S 3 are turned ON.C 2 is discharged through the diode D 2 to obtain a voltage level of -2V dc /3.The operation of mode 6 is shown in Fig. 6 Mode 7: In mode 7 operation, switch S S1 of the capacitor selection circuit is turned ON and S 3 and S 2 of the full bridge power converter is turned ON to obtain the voltage level of V dc. The equivalent circuit of mode 7 is shown in Fig. 6(c) Mode 8: In mode 8 operation, all the switches of inverter circuit are turned OFF to get the zero output. The operation of mode 8 is shown in Fig. 6(d) Fig.7 Simulation circuit of Conventional Interleaved Boost Converter Simulink model of soft switching interleavedboost converter with topology 1 and topology 2 is shown in Fig.8 and Fig.8 Simulation circuit of topology 1 and topology 2 Fig.9 shows input voltage of 48V for the interleaved boost converters and Fig. 9 shows the gate pulses for the switches S 1 and S 2.Fig. 10 and shows the output voltage and output power of conventional interleaved boost converter. (c) (d) Fig. 6 Operation of different modes in negative half cycle Mode 5 mode 6 (c) mode 7 (d) mode 8 III. SIMULATION RESULTS Simulation of the proposed seven level inverter was done in MATLAB/ Simulink. The generalized PV model, conventional interleaved boost converter, proposed soft switching interleaved boost converter

53 Fig. 9 Input voltage and gate trigger pulses for the switches Fig.11 Output voltage and Output power of topology 1 The output voltage of 94V is obtained for an input voltage of 48V and it is shown in Fig.12 Fig.12 shows the output power waveform of topology 2 Fig. 10 Output voltage and Output power of conventional Interleaved boost converter The output voltage of 114V is obtained for topology 1 with input voltage of 48V and it is shown in Fig.11. Fig.11 shows the output power waveform of topology 1. Fig.12 Output voltage and Output power of topology 2 COMPARISON RESULTS Table 1 shows the output voltage comparison results of different interleaved boost converter topologies. From the obtained results it is concluded that topology 1 has high voltage gain when compared to topology 2

54 TABLE 1: Output voltage comparison of two interleaved boost converters Table 2 shows the efficiency comparison results of different interleaved boost converters. The obtained results shows that topology 2 has better efficiency when compared to topology 1 and the efficiency increases in the order of 0.65 to 0.75% Fig.14 Solar input Output voltage of topology 2 Fig.15 shows the carrier and reference signal of phase disposition PWM technique. Fig.15 shows the variable frequency inverted sinusoidal PWM technique. TABLE 2: Efficiency comparison results of two interleaved boost converters Fig.13 shows the Simulink model of seven level inverter. Fig.14 and shows the solar input and interleaved boost converter output voltage. Fig.13 Proposed Seven Level Inverter with Topology 2 Fig.15 Phase disposition PWM and Variable Frequency Inverted Sinusoidal PWM techniques Fig.16 and shows the seven level output voltage and FFT analysis for Phase Disposition PWM technique with THD of 23.03%

55 that topology 1 gives high voltage gain and topology 2 results in better efficiency which increases in the order 0.65 to 0.75% when compared to topology 1. Fig.16 Seven Level output FFT analysis (Phase Disposition PWM technique) Fig.17 and shows the seven level output voltage and FFT analysis for variable frequency inverted sinusoidal PWM technique with THD of 25.54% Fig.17 Seven Level output FFT analysis (Variable frequency inverted sinusoidal PWM technique) IV. CONCLUSION The circuit model involves a seven level inverter which is fed by solar source through soft switching interleaved boost converter. The performance of seven level inverter was analysed my means of Multicarrier Sinusoidal Phase Disposition Pulse Width Modulation (MCSPDPWM) and Variable Frequency Inverted Sinusoidal Pulse Width Modulation (VFISPWM) technique. The obtained Total Harmonic Distortion (THD) results are 23.03% for MCSPDPWM and 25.54% for VFISPWM techniques respectively. The different topology operation of soft switching interleaved boost converters are simulated and compared with conventional interleaved boost converter. From the obtained results it is concluded REFERENCES [1] J. Chavarria, D. Biel, F. Guinjoan, C. Meza, and J. J. Negroni, Energy balance control of PV cascaded multilevel grid-connected inverters under level-shifted and phase-shifted PWMs, IEEE Trans.Ind.Electron.,Vol. 60,no.1,pp. 98 111,Jan. 2013. [2] S. Choi and M. Saeedifard, Capacitor voltage balancing of flying capacitor multilevel converters by space vector PWM, IEEE Trans. Power Delivery, Vol. 27, no. 3, pp. 1154 1161, Jul. 2012. [3] K. Hasegawa and H. Akagi, Low modulation index operation of a five level diode clamped PWM inverter with a dc- voltage balancing circuit for a motor drive, IEEE Trans. Power Electron.,Vol.27,no.8,pp.3495-3505,Aug.2012 [4] Jinn Chang Wu, Chia-Wei Chou, A Solar power generation system with a seven - level inverter IEEE Trans. Power Electronics,Vol.29,No.7,July 2014. [5] J.Mei,B.Xiao, K.Shen, L.M.Jian Yong Zheng, Modular multilevel inverter with new modulation method and its application to photovoltaic grid - connected generator IEEE Trans. Power Electron., Vol.28, no.11, pp.5063-5073, Nov.2013. [6] Y.Ounejjar, K. Al Hadded and L.A. Dessaint A novel six band hysteresis control for packed U-cells seven level converter: Experimental validation. IEEE Trans. Ind. Electron., Vol.5, no.10, pp.3808-3816, Oct.2012 [7] J.Pereda and J. Dixon, High- frequency link: A solution for using only one DC source in asymmetric cascaded multilevel inverters IEEE Trans. Ind. Electron., Vol.58, no.9, pp. 3884-3892, Sep.2011. [8] N.A.Rahim, K.Chaniago and Selvaraj, Single phase seven level grid-connected inverter for photovoltaic system, IEEE Trans. Ind.Electr., vol.58 no.6, pp. 2435 2443, Jun.2011 [9] A.K Sadigh, S.H.Hosseini, M. Sabahi, and G.B. Gharehpetian, Double flying capacitor multicell converter based on modified phase shifted pulse width modulation IEEE Trans. Power Electron., Vol. 25,no.6,pp.1517-1526, Jun.2010 [10] J. Selvaraj and N. A. Rahim, Multilevel inverter for grid-connected PV system employing digital PI controller, IEEE Trans. Ind. Electron., Vol. 56, no. 1, pp. 149-158, Jan. 2009. [11] X.She, A. Q. Huang, T. Zhao, and G. Wang, Coupling effect reduction of a voltage-balancing controller in single-phase cascaded multilevel converters, IEEE Trans. Power Electron., Vol. 27, no. 8, pp. 3530 3543, Aug.2012.

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