Harmonic minimization in multilevel inverters using selective harmonic elimination PWM technique

Abstract

Generally the output voltage of the inverters must be sinusoidal. However the waveforms of practical inverters are non sinusoidal and contain certain harmonics. For low and medium power applications, square wave or quasi square wave may be acceptable but for high power applications, low distorted sinusoidal waveforms are required. By increasing number of levels in inverter the output voltage have more steps generating a staircase waveform, which has reduced harmonic distortion. There emerges need of multilevel inverter. In this paper cascaded multilevel inverter with Selective Harmonic Elimination Pulse Width Modulation (SHE-PWM) technique is implemented. The problem of SHE-PWM is to solve the non linear transcendental equations which are used to determine the switching angles. Here the evolutionary algorithm based on natural selection is proposed to solve the equations which reduce the computational burden resulting in faster convergence. The main advantages are reduced total harmonic distortion and low switching frequency. To validate the computational results for switching angles, a simulation is carried out in MATLAB/SIMULINK software tool for a 7-level cascaded H-bridge inverter.