Abstract

This paper presents the application of direct torque control in an induction motor, using a multilevel cascaded inverter with separated dc sources. The control strategy operates with imposed switching frequency, improving torque behavior. The paper studies the theoretical concepts related to this method, like vector selection, state variables estimation, and commutation time calculation. In addition, this paper presents results for a three- and 11-level inverter-fed drive, from which it can be appreciated that the increase of levels of the load voltage reduces the torque ripple. © 2004 IEEE.