Implementation of direct torque control of AC drive with synchronized notched DC link voltage

In this paper a quasi-parallel resonant inverter is used to implement the DTC strategy of induction motor drive to obtain a high performance AC drive. This scheme combines the advantages of quasi-parallel resonant inverter (operation at high switching frequency, high efficiency, and reduced EMI) and those of the DTC (good dynamic performance and fast response of torque and flux). The DC link voltage is pulled down to zero when any inverter switch has to change its switching state. Thus, the DTC algorithm can be implemented with zero hysteresis band of both torque and flux controllers to enhance the DTC performance. Simulation and experimental verification are presented. Good trace of motor torque and flux are obtained.