Design, Implementation and Control of a Multilevel Cascade Inverter for AC Drive Application with Improved Low Speed Operation

AC electric drives today are widely used in small and large industries to start up and control single-phase and three-phase AC motors. During the start-up period, these drives should limit the current magnitude in addition to maintaining torque. It must also be able to control the speed of the motor in a steady state with the electrical and mechanical parameters that meet the standards at the same time. In this paper, some of the standards for adjustable speed AC drives are first reviewed. Then the design and implementation process of a low voltage/ medium power multilevel inverter is briefly explained. Some electrical/ mechanical constrains that an AC motor drive should satisfy are extracted from the standard. Then a hybrid control algorithm is proposed for low speed and high speed operation which is simple and efficient. Simulation and experimental results on a 400 V three phase 5 hp induction motor is presented to evaluate the design.