Torque and Flux Ripple Elimination in DTC Control of PMSM Motors using Duty Cycle Control of Voltage Vectors

This paper presents a novel method for controlling torque and stator flux ripples in DTC control of PMSM motor. In contrast to conventional duty ratio modulation methods which do not pay attention to stator flux condition, the proposed method controls both torque and stator flux RMS ripples using minimization of a proper two variable (stator flux and torque) objective function. After realizing that, flux related machine specifications such as circular stator flux vector trajectory and current waveform quality will be developed. For this purpose, in addition to torque dynamics in any DTC control cycle, stator flux dynamics will be studied. Using this, the condition of both torque and stator flux at the end of an applied voltage vector of inverter is predicted. Then, standard deviation of torque RMS ripple and that of stator flux is studied in any control cycle and the normalized sum of these two deviations will be considered as the objective function. Finally, a proper switching instant during any control cycle is calculated for minimizing the objective function. The proposed method is validated by MATLAB simulation.