New Optimal Current Control Strategy for Six-Phase DC-Biased Vernier Reluctance Machines Considering Distorted EMF

The distorted back electromotive force (EMF) waveforms of dc-biased vernier reluctance machines result in stator current distortion, torque ripple, and efficiency reduction. For the purpose of eliminating the harmonic currents and optimizing the phase current, a new optimal current control strategy is proposed by utilization of accurate fundamental and harmonic voltage equations. Each harmonic component is decoupled in the multilevel synchronous rotating coordinate. The interactions between the multiple harmonic currents are avoided, and it assures a strong robustness. The harmonic currents can be suppressed significantly both in steady-state and dynamic operation, and it has a positive effect on the efficiency and torque ripple. Furthermore, a modified maximum torque per ampere curve considering inductance nonlinearity is achieved by adjusting the dc-ac current ratio under different phase currents, aiming to maximize the output capacity. Finally, the effectiveness of the proposed optimal current control strategy is validated experimentally for a prototype machine.