Direct torque control with improved speed controller for 18-pulse ATRU-VSI-fed PMSM drive system

An 18-pulse autotransformer rectifier unit (ATRU) - voltage source inverter(VSI)-fed permanent magnet synchronous machine (PMSM) drive system with direct torque control (DTC) scheme is presented in this paper. An improved speed controller in terms of acceleration, constant-speed and braking modes is proposed in the DTC drive system instead of conventional PI regulator. Moreover, maximum torque per ampere (MTPA) control for constant torque operation and flux weakening (FW) control for constant power operation are applied both in accelerating and braking mode. The simulation and analysis results indicate that ac-side power factor is close to unit and the DC bus voltage ripple is restrained. Moreover, the transition among three modes is rather smooth, and almost no overshoot in the speed response. Also smaller torque pulsation and better steady and dynamic responses are obtained by means of the proposed speed controller.