Comparison between 7-Level Cascaded and 7-Level Diode-Clamped Multilevel Inverters for Feeding Induction Motor

In this study, two types of multilevel convertors, cascaded multilevel inverter with separate DC sources and diode clamped multilevel inverter with common DC source are modeled and compared in the case of feeding of an induction motor. Here, SHEPWM technique is used as the switching strategy. Also a new variable torque feedback control on modulation index is presented, to preserve the induction motor in stable condition. Furthermore, the merits and demerits of each convertor from power quality point of view are compared. Outputs of simulations shows that despite of that feeding of loads using diode clamped multilevel convertors with common dc source is easier than cascaded converters from feeding inverters with DC sources point of view, even thought cascaded multilevel inverters has more robust performance in case of feeding variable torque induction motor loads. And our feedback controller works to improve outputs of multilevel inverter and parameters of induction motor in both cases.