New direct torque control of asynchronous motor with low ripple in torque and current, and quick response

In traditional direct torque control, there is usually undesired torque and current ripple, variable switching frequency and acoustic noises. A new direct torque control method is proposed in this paper. By analyzing the effect of voltage vector on the stator flux and electromagnetic torque under consideration of the voltage drop on the stator resistance, one can point out that the necessary condition for the increase of torque and the critical condition of the flux change are neglected, on the basis of above analysis, then a new voltage vector selection table is proposed. The amplitude of the commanding voltage vector depends on the duty ratio which is derived from the errors of torque and flux only. The duty ratio is simplified by using a two-step design minimum torque ripple in this paper. Simulation and experimental results are illustrated confirming the correctness and validity of theoretical analysis and that the torque and current ripple are reduced while response time of the control system is increased in this paper.