Switching-table-based direct torque control of dual three-phase PMSMs with closed-loop current harmonics compensation

In this paper, 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 (dual 3-ph PMSMs). 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 backelectromotive force distortion, which are also mapped into the x-y subspace. Therefore, in this work the x-y voltage references are obtained by the closed control loop that controls x-y currents to zero. To modulate the non-zero x-y voltage reference, the new modulation approach employing voltage vector groups in 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 twelve voltage vector groups illustrates a trade-off between linear range in 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.