Switching-Table-Based Direct Torque Control of Dual Three-Phase PMSMs With Closed-Loop Current Harmonics Compensation

In this article, the new closed-loop current harmonics compensation strategy is introduced in the switching-table-based direct torque control (ST-DTC) of dual three-phase permanent magnet synchronous machines. The harmonic current distortion is the major problem of ST-DTC of multiphase machines and is typically caused by the lack of control in the auxiliary x-y subspace under the vector space decomposition model. The synthetic vectors to obtain average zero voltage in the x-y subspace can be a solution. However, this cannot compensate for current harmonics; for example, due to dead-time and back-electromotive force distortion, which is also mapped into the x-y subspace. Therefore, in this article, the x-y voltage references are obtained by the closed control loop that controls x-y currents to zero. To modulate the nonzero x-y voltage reference, the new modulation approach employing voltage vector groups in the x-y subspace together with the new switching table is developed and incorporated into ST-DTC. Meanwhile, the analysis of the two available sets of 12 voltage vector groups illustrates a tradeoff between linear range in the x-y subspace and the dc-link voltage utilization rate. Finally, the effectiveness of the proposed ST-DTC strategy is verified through experiments and simulation.