An high performance direct torque control method with PWM approach of PMSMs

PMSM(Permanent Magnet Synchronous Motor)s are much widely used in the control systems of the industrial application and robotics due to the high control performance and high power density with high efficiency. For the torque control of PMSM, direct torque control(DTC) schemes are much interested due to the easy implementation and fast dynamic response. Though its fast dynamic response, high torque and flux ripples with random switching frequency are still a major drawback to be applied to the practical system. The DTC-PWMs(Direct Torque Control-Pulse Width Modulation) are good choice to overcome the higher ripple and random switching. The duty ratio calculation algorithm of DTC-PWMs is the most important to advance the control performance. This paper presents a high performance a Direct Torque Control with PWM approach based on the approximate voltage function. In the proposed control scheme, 12-side sectors division is used to reduce the torque angle variation based on the supplied voltage analysis. And the voltage vector selection is determined by the error level selector of the flux and torque. Unlike the CDTC-PWMs(Conventional DTC-PWM), three different voltage vectors can be selected according to the flux and torque error level. The proper voltage vector among three different voltage vectors is determined by the designed error level selector to reduce torque and flux ripple with fast dynamic response. For the calculation of the PWM duty ratio, the approximated voltage functions based on the d-q voltage analysis of the selected voltage vector are proposed in this paper. And the approximated voltage functions which are described as voltage angle are used as the denominator of the duty ratio calculator. The duty ratio of the proposed method uses the flux and torque ripple with speed information using approximated voltage functions. The proposed control scheme is verified by the experiments using the proto-type PMSM.