Direct Torque Control for VSI-PMSM Using Vector Evaluation Factor Table

In this paper, a direct torque control (DTC) using vector evaluation factor table (VEF-Table) is proposed for voltage source inverter (VSI)-permanent magnet synchronous motor (PMSM) drive system. In this approach, the candidate vectors can expand from six active vectors to3× Ndvectors with duty cycle, and the change trends of torque and flux generated by all candidate vectors can be quantified and stored in the VEF-Table offline. In order to choose the output vector from the VEF-Table, a “Two-Step” selection algorithm is established based on the cost function, which can select two vectors with duty cycle sequentially. By synthesizing two vectors, the proposed approach is capable of adjusting the magnitude and angle of the output vector, so as to reduce the undesirable ripples of torque and flux. The feasibility and effectiveness of the proposed approach is verified by both numerical simulations and experimental results.