High performance torque and flux control for multilevel inverter fed induction motors

This paper presents a high performance torque and flux control strategy for high power induction motor drives. The control method uses the torque error to control the load angle, obtaining the appropriate flux vector trajectory from which the voltage vector is directly derived based on DTC principles. The voltage vector is then generated by an asymmetric cascaded multilevel inverter without need of modulation. Due to the high output quality of the inverter, the torque response presents nearly no ripple. In addition, switching losses are greatly reduced since 80% of the power is delivered by the high power cell of the asymmetric inverter, which commutates only a few times per cycle. Simulation and experimental results for a 81-level inverter are presented.