Modified frequency carriers for improving DTC with constant frequency torque controller of induction machines

Constant frequency torque controller-based direct torque control (CFTC-DTC) of an induction motor (IM) drive has been widely studied for two- and multi-level voltage source inverter recently. This control method suffers from the limitation of torque loop bandwidth since the frequency carriers are generated by the same software used for system control. The performance of CFTC depends mainly on the torque loop bandwidth; the higher the bandwidth, the better the performance of CFTC-DTC drive. This paper proposes a modification on the frequency carriers of CFTC to increase the torque loop bandwidth. Unlike the conventional CFTC, the carriers of proposed CFTC are generated by ramp waveforms resulting in 50 % increase of the carrier frequency. The simulation results prove the effectiveness of the proposed drive system.