Modified Direct Torque Control for Fast Dynamics PMSM Drives fed by Three-Level NPC Inverter

This paper proposes a simple control method for improving direct torque control (DTC) of permanent-magnet synchronous motor (PMSM). Although conventional torque regulator minimizes torque ripples and fixes switching frequency, it has a slow torque dynamics especially in low-speed region. This is due to the utilization of small voltage vectors during torque increment. The small voltage vectors have a small duty-cycle, which is very useful in torque ripple reduction during steady-state operation of the PMSM. However, these small voltage vectors are short compared to large voltage vectors in shorten the settling-time during dynamic operation of the PMSM especially in low-speed region. Therefore, a proposed torque regulator is used during transient-state operation of PMSM with large duty-cycle to achieve fast-dynamic response, while maintaining the conventional torque regulator merits in minimizing torque ripples during steady-state operation. Simulation results are presented to prove the effectiveness of proposed method.