CONTROL TECHNIQUES FOR VARIOUS BIPOLAR PWM STRATEGIES OF THREE PHASE FIVE LEVEL CASCADED INVERTER

Abstract

This paper presents different types of bipolar Pulse Width Modulation (PWM) strategies for the chosen Cascaded MultiLevel Inverter (CMLI). The main purpose of MLI is to use power semiconductor devices of lower voltage ratings to realize high voltage levels at inverter output. Due to their ability to obtain refined output voltage waveforms, reduced Total Harmonic Distortion (THD) and reduced EMI problems by reducing the switching dv/dt. In this paper, a three phase CMLI is controlled with Sinusoidal PWM strategy with Phase Disposition PWM (PDPWM), Phase Opposition and Disposition PWM (PODPWM), Alternative Phase Opposition and Disposition PWM (APODPWM), Phase Shift PWM (PSPWM) and hybrid modulation strategy and the variation of THD in their outputs are observed by varying the modulation index. Simulations are performed using MATLAB-SIMULINK. It is observed that APODPWM and PSPWM provide output with relatively low distortion. It is also seen that PS, APOD and hybrid PWM are found to perform better since they provide relatively higher fundamental RMS output voltage. From hardware results it is seen that POD PWM provides output with relatively low distortion. It is also observed that PSPWM is found to perform better since it provide relatively higher fundamental RMS output voltage.

Keywords

• Total Harmonic Distortion
• Cascaded multi level inverter
• Phase disposition
• Phase opposition and disposition
• Alternative phase opposition and disposition
• Field Programmable Gate Array