Optimum Switching Angles For Multilevel SHE-PWM Inverter Using Genetic Algorithm

Abstract

An attempt is made to develop an 11-level inverter (single-phase) with almost sinusoidal waveform by the use of programmed Pulse Width Modulation or SHEPWM technique and Genetic Algorithm for eliminating mostly injurious lower order harmonics. An ideal inverter which drives a load should give sinusoidal output voltage as rating of load is indicated by the manufacturer on the basis of sinusoidal input. The rectangular waveform of conventional full-bridge voltage source inverter not only reduces efficiency of the load equipments but also reduces their longevity due to presence of lower and higher order harmonics in addition to fundamental. Although, the pattern of both the output voltage and current waveforms with minimum ripple can be improved with the help of high frequency switching by way of various conventional PWM techniques but with increase in switching losses and electromagnetic interference. The harmonic effect can also be reduced by using large size filter (as harmonic frequencies are on the lower side) which increases the cost of inverter as well as its size. The problem can also be solved to a great extent by replacing conventional two-level inverters with multilevel inverters which use lower switching frequencies to switch ON and switch OFF the power devices and give better total harmonic distortion (THD) even without use of filter.Genetic Algorithm has been used for finding switching/firing angles for the power devices by solving related mathematical equations (which are nonlinear in nature) with a view to remove the selective harmonics. As the most dominating harmonics are shifted on the higher frequency side, their effect can be reduced by use of smaller size filter, if required.