A Duty Ratio Control Strategy to Reduce Both Torque and Flux Ripples of DTC for Permanent Magnet Synchronous Machines.

This paper proposes a novel duty ratio modulated direct torque control (DDTC) for permanent magnet synchronous motor drive system to achieve high steady performance and reducing ripples of CDTC, especially the ripple of stator flux, which is ignored in the conventional DDTC. The proposed control scheme incorporates the variation rates of current and conventional duty ratio modulation. By introducing the instantaneous variation rates of d-axis current and q-axis current during each sampling cycle into the conventional DDTC, an effective duty ratio modulation method is constituted to determine the time duration of the active voltage vector. Moreover, based on the characteristics of the proposed duty ratio modulation, a weighting coefficient is utilized to improve the performance of the duty ratio modulation. The proposed method can reduce the ripple of torque and stator flux significantly, as well as reduce the ripple of d-q-axis current. The proposed method can achieve a good performance of the steady operation. The simulations and experimental results validate the effectiveness of the proposed schemes.