COMPARISON OF DIFFERENT TECHNIQUES FOR SELECTIVE HARMONIC ELIMINATION PWM IN INVERTERS - A REVIEW

Conventional single phase inverter offers a square wave output which when applied to electrical appliances may damage the later reducing its efficiency and life as this inverter output waveform is not sinusoidal and contains lower and higher order harmonics in addition to fundamental. On the other hand Selective Harmonic Elimination with Pulse Width Modulation (SHE-PWM) offers a fine control of the harmonic spectrum of a given voltage and/or current waveforms generated by a DC to AC converter (inverter). Inverters with this technique operate with low switching frequencies and due to capability of elimination of lower order harmonics, SHE-PWM is highly advantageous for high power inverters over other techniques that reduces the harmonics as a whole and generate high-quality output which in turn results in minimum current ripple, reduced torque pulsations, improved overall performance by increasing the life and efficiency of the electrical appliances. Over the last few years, the SHE-PWM technique is extended from low level inverters to multilevel inverters. This paper provides a comprehensive study of different SHE-PWM techniques as well as different solving algorithms for finding out solution of a set of nonlinear transcendental equations and implementation of the same in various multilevel inverter topologies, like Diode-clamped MLI, Flying-capacitor MLI and Cascaded H-Bridge MLI.