Analysis of induction motor by using cascaded multilevel inverter

Abstract

Multilevel inverters had gain popularity over the years in industrial applications such as motor drives, static VAR compensators and renewable energy system. Multilevel inverters have received this attention as it promises less disturbance and possibility to function at lower switching frequency than traditional two level inverters. Out of many level inverters topologies proposed, cascaded multilevel inverters features a high modularity degree because each inverter can be seen as a module with similar circuit topology, control structure and modulation. With large numbers of advantages CMI has one major limitations of voltage unbalance across the dc capacitor. This thesis explores basis structure and operating principles of CMI. Common modulation techniques are summarized. This thesis also presents the total harmonics distortion (THD) analysis of seven level CMI with phase shifted (PS) sinusoidal pulse width modulation (SPWM) and level shifted (LS) SPWM techniques such as phase disposition (PD), phase opposition disposition (POD), and alternate phase opposition disposition (APOD). The harmonic spectrum for PS and LS SPWM techniques are compared. Module capacitor voltage balancing algorithm such as sorting strategy is proposed for CMI.