PERFORMANCE ANALYSIS OF SEVEN LEVEL INVERTER … · PERFORMANCE ANALYSIS OF SEVEN LEVEL INVERTER WITH ... generated by the solar cell array into ac power and ... generation of gate

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50 International Journal of Scientific Research Engineering & Technology (IJSRET), ISSN 2278 – 0882

Volume 4, Issue 1, January 2015

PERFORMANCE ANALYSIS OF SEVEN LEVEL INVERTER WITH

SOFT SWITCHING CONVERTER FOR PHOTOVOLTAIC SYSTEM

M.Vidhya1, Dr.P.Radika

2, Dr.J.Baskaran

3

1PG Scholar, Dept.of EEE, Adhiparasakthi Engineering College, Melmaruvathur, Tamilnadu, India 2Professor, Dept.of EEE, Adhiparasakthi Engineering College, Melmaruvathur, Tamilnadu, India

3HOD, 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

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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

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. 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

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 C1 and output from the converter is given to

the capacitor C2.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.4 Circuit Diagram of Seven Level Inverter with

Topology 2

The output voltage of the seven level inverter has

the following voltage levels: Vdc, Vdc/3, 2Vdc/3, 0,-

Vdc/3,-2Vdc/3,-Vdc .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 SS1 and

SS2 of the capacitor selection circuit are turned OFF.S1

and S4 switches of the full bridge power converter are

turned ON and C1 is discharged through diode D1 to

obtain a voltage level of Vdc/3.The operation of mode 1

is shown in Fig.5(a)

Mode 2: In mode 2 operation, SS2 of the capacitor

selection circuit and S1 and S4 of the full bridge power

converter is ON and C2 is discharged through the diode

D2 toobtain a voltage level of 2Vdc/3.The equivalent

circuit of mode 2 is shown in Fig.5(b)

Mode 3: In mode 3 operation, in the capacitor selection

circuit SS1 is ON.S1 and S4 of the full bridge power

converter is turned ON to obtain Vdc 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)

(a) (b)

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(c) (d)

Fig. 5 Operation of different modes in positive half

cycle (a) Mode 1 (b) 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(a)

Mode 6: In mode 6 operation, switches SS2, S2 and S3

are turned ON.C2 is discharged through the diode D2 to

obtain a voltage level of -2Vdc/3.The operation of

mode 6 is shown in Fig. 6(b)

Mode 7: In mode 7 operation, switch SS1 of the

capacitor selection circuit is turned ON and S3 and S2

of the full bridge power converter is turned ON to

obtain the voltage level of –Vdc. 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)

(a) (b)

(c) (d)

Fig. 6 Operation of different modes in negative half

cycle (a) Mode 5 (b) 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

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.

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 (a) and (b)

(a)

(b)

Fig.8 Simulation circuit of (a) topology 1 and (b)

topology 2

Fig.9 (a) shows input voltage of 48V for the

interleaved boost converters and Fig. 9(b) shows the

gate pulses for the switches S1and S2.Fig. 10(a) and (b)

shows the output voltage and output power of

conventional interleaved boost converter.

(a)

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(b)

Fig. 9(a) Input voltage and (b) gate trigger pulses for

the switches

(a)

(b)

Fig. 10(a) Output voltage and (b) 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 (a). Fig.11 (b) shows the output power

waveform of topology 1.

(a)

(b)

Fig.11 (a) Output voltage and (b) 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 (a) Fig.12 (b)

shows the output power waveform of topology 2

(a)

(b)

Fig.12 (a) Output voltage and (b) 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

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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%

TABLE 2: Efficiency comparison results of two

interleaved boost converters

Fig.13 shows the Simulink model of seven level

inverter. Fig.14 (a) and (b) shows the solar input and

interleaved boost converter output voltage.

Fig.13 Proposed Seven Level Inverter with Topology 2

(a)

Fig.14 (a) Solar input (b) Output voltage of topology 2

Fig.15 (a) shows the carrier and reference signal of

phase disposition PWM technique. Fig.15 (b) shows

the variable frequency inverted sinusoidal PWM

technique.

(a)

(b)

Fig.15 (a) Phase disposition PWM and (b) Variable

Frequency Inverted Sinusoidal PWM techniques

Fig.16 (a) and (b) shows the seven level output voltage

and FFT analysis for Phase Disposition PWM

technique with THD of 23.03%

(a)

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(b)

Fig.16 (a) Seven Level output (b) FFT analysis (Phase

Disposition PWM technique)

Fig.17 (a) and (b) shows the seven level output

voltage and FFT analysis for variable frequency

inverted sinusoidal PWM technique with THD of

25.54%

Fig.17 (a) Seven Level output (b) 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

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.

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PERFORMANCE ANALYSIS OF SEVEN LEVEL INVERTER … · PERFORMANCE ANALYSIS OF SEVEN LEVEL INVERTER WITH ... generated by the solar cell array into ac power and ... generation of gate