Despite the robustness and fast dynamic response, direct torque control (DTC) exhibits relatively large ripples in torque and flux during steady-state operation. Mitigating these ripples depends on designing a pulse selector to identify the optimal voltage vector at every control cycle, which has been reported with different structures in the literature. Hence, it is becoming increasingly crucial to comprehensively understand the criteria used in pulse selection and analyze their impact on the overall DTC performance. These are challenging in permanent magnet synchronous motor (PMSM) drives due to the nonlinear torque/current characteristics and spatial harmonics of the magnetic flux. This paper exploits the high fidelity and computational efficiency of the finite-element analysis (FEA)-based model to present a performance prediction strategy for DTC of PMSM under different pulse selectors. First, this model is employed to thoroughly analyze the influence of each switching pulse on the torque and flux deviations under changing operating conditions considering the machine's nonlinearities. Then, the pulse selection schemes used in switching-table-based DTC are comparatively evaluated, highlighting the advantages and limitations of each. Based on this evaluation, an advanced pulse selector with a variable-structure switching table (VSST) is developed, reducing torque/flux ripples and simplifying the control implementation while maintaining the fast dynamic response of DTC.
- Direct torque control (DTC)
- finite-element analysis (FEA)
- permanent magnet synchronous motor (PMSM)
- pulse selection
- torque ripple