Multilevel Voltage Source Inverter for Grid Connected Photovoltaic System

Multilevel VOLTAGE SOURCE Inverter for Grid Connected Photovoltaic System

PRESENTED By; Imtiyaz sayyed

Department of Electrical Engineering

INTRODUCTION

The conventional energy sources are fast depleting these days. So the demand for renewable energy sources has been increased.

The power developed by photovoltaic system is DC. To convert this DC power a photovoltaic inverter is used.

Improving the output waveform of the inverter helps to reduce the harmonic content in the current injected into the grid in a grid connected system.

What is Multilevel Inverters?

A multilevel inverter is a power electronic device which is capable of providing desired alternating voltage level at the output using multiple lower level DC voltages as an input. 

What is Two level Inverter?

The voltage source inverters produce a voltage or a current with levels either 0 or ±Vdc they are known as two level inverters.

Fig. Three, Five, Seven Multilevel inverter waveform switched at fundamental frequency

 CONCEPT OF MULTILEVEL INVERTER

A two-level Inverter creates two different voltages for the load

 few drawbacks as it creates harmonic distortions in the output voltage and also has a high dv/dt as compared to that of a multilevel inverter

The concept of multilevel Inverter (MLI) is kind of modification of two-level inverter

the output waveform obtained in this case has lower dv/dt and also lower harmonic distortions

Smoothness of the waveform is proportional to the voltage levels

Fig. 1 Equivalent circuit of solar cell

MODELING OF PV MODULE

Here

Ig = light generated current Rsh = Shunt resistance Rs = Series resistance Id = Diode current

SINGLE PHASE FIVE LEVEL INVERTER

Fig. 2 Single phase five level inverter topology

The operating principle of the inverter is to generate five levels of voltage. i.e., Vin, Vin/2, 0, -Vin/2, -Vin.

The pulse width modulation scheme for the five level inverter is as follows:-Two reference signals Vref1 and Vref2 are compared with a high frequency carrier signal, Vtri at the same time.

Fig. 3 Switching pattern for the single phase five level inverter

Table I Inverter output voltage during switches S1-S5 on and off

Fig.4 Grid voltage and Grid current using conventional H-bridge inverter

Fig.5 Grid voltage and Grid current using five level inverter

CONCLUSION

In these days of fast depleting conventional energy sources, photovoltaic systems are a very good alternate. Here a grid connected photovoltaic system is simulated in MATLAB.

From the simulation results it was observed that the using multilevel inverters in such grid connected PV system considerably reduces the THD level of the current injected into the grid.