New simplified controlling techniques for multilevel inverter in DC AC conversion

Abstract

In recent years, high power electronic converters play a major role in renewable energy resources to get maximum available power. A group of power semiconductor switches form large numbers of converters. Multi Level Inverter (MLI) is one which converts dc input of fixed value into ac output with stepped waveform. The multilevel inverters are formed by combining semiconductor switches, dc voltage sources, capacitors and diodes. Consider that n is the number of level of phase voltage with respect to negative terminal then the number of levels of the inverter is 2n+1. By increasing the number of levels of stepped voltage the harmonics of the output voltage is decreased. However, generating control signals to the switches of the MLI becomes complex. The basic types of multilevel inverters are diode clamped multilevel inverter, flying capacitor multilevel inverter and cascaded multilevel inverter. The advantages of the multilevel inverters are low output voltage distortion, lower voltage stress dv/dt, low distortion in input current, smaller common mode voltage and it can be operated in low switching frequency. Several controlling techniques are available to generate control signals. The common controlling techniques are Triangular carrier based schemes, hysteresis current control, delta modulation, space vector based algorithm, carrier based harmonic elimination schemes, stepped waveform synthesis and Pulse Width Modulation (PWM) schemes. newlineIn the proposed research work a nine level simplified multilevel inverter is implemented. This simplified nine level MLI consists of one dc voltage source, seven switches, four capacitors and twelve diodes. The four capacitors share the input dc voltage equally. newline newline newline