Six-Step Operation of a Symmetric Dual Three-Phase PMSM With Minimal Circulating Currents for Extended Speed Range in Electric Vehicles

Automotive applications demand high efficiency, good reliability, and a wide operating speed range within limited DC bus voltage constraints. In this paper, a zero degree displacement dual three-phase PMSM is derived from an original 3-phase PMSM to enhance the power rating as well as the operating speed range. The proposed topology can be used as an alternative to the conventional configuration of three-phase PMSM with a bidirectional DC-DC converter for electric vehicles. Even though the commonly used dual three-phase PMSM with split-phase winding eliminates the sixth harmonic torque pulsation, a large circulating current is generated during six-step operation, which results in additional stator copper loss. In this paper, six-step operation of the symmetric dual three-phase PMSM with zero degree winding displacement is proposed to achieve maximum inverter utilisation. Both harmonic circulating current and torque pulsation were observed to be within satisfactory levels using this configuration. A changeover algorithm is also proposed to enable a smooth transition between closed-loop current vector control during low and medium speed operation to open-loop six-step voltage angle control for high speed operation. The performance of the proposed method is experimentally validated on a 3kW dual three-phase PMSM drive.