A Novel Switching-Table-Based Direct Torque Control With Improved Current and Torque Steady-State Performance for Dual Three-Phase PMSM

The classical switching-table-based direct torque control (ST-DTC) suffers from issues such as large torque ripples, significant current harmonics, and variable switching frequency. In this article, a novel ST-DTC is proposed to improve the current and torque steady-state performance for dual three-phase permanent magnet synchronous motor (DTP-PMSM). First, proportional resonance (PR) controllers are used in the
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subspace, and the
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reference voltage generated by PR controllers is modulated by three fixed vectors based on the analysis of flux and torque slopes of voltage vectors with different amplitudes. This reduces current harmonics and computational burden of modulating the
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reference voltage. Second, duty-ratio modulation is employed to reduce the torque ripple. However, under the traditional torque regulator, the duty-ratio modulation exists a torque range where it cannot achieve the instantaneous zero error of torque at the end of the control period. Therefore, the feedback value of the torque regulator is modified to further suppress torque ripple. Furthermore, to prevent generating incorrect switch sequences caused by the short dwell time of vectors and maintain the thermal balance of the inverter, an optimization of the switching sequence is performed. Finally, experimental results are presented to validate the effectiveness of the proposed method.