Duty-Ratio-Based Direct Torque Control With Enhanced Harmonic Current Suppression for Dual-Three-Phase Permanent Magnet Motor

This article proposes a new duty-ratio-based direct torque control (DR-DTC) with enhanced harmonic current suppression for a dual-three-phase permanent magnet (DTP-PM) motor. First, a new virtual voltage vector construction method based on the carrier-based modulation technique is proposed. Twelve virtual voltage vectors with null average voltage values in two harmonic subspaces are constructed. The sequences of the constructed virtual voltages can be calculated directly in the natural coordinate system. In addition, the whole sequences are standard symmetrical, which can be easily generated by a digital controller. After that, an online harmonic current compensation method is investigated. Additional controllers compensate for the harmonic currents induced by the back electromotive force and nonlinear factors. Since the virtual voltage vectors have null average voltage values in two harmonic subspaces and the online harmonic current compensation method is designed, the proposed DR-DTC can be introduced to the DTP-PM motor with a single neutral point and two neural points. With the proposed strategy, the capability of harmonic current suppression can be significantly improved, and the processes of virtual voltage construction can be simplified. In addition, the advantages of the conventional DR-DTC can be inherited. Finally, experiments are carried out to validate the feasibility of the proposed strategy.