Flux Weakening Control Strategy for Asymmetric Surface Inset Permanent Magnet Synchronous Motors Based on Reoriented dq-Axis Reference Frame

In this article, a novel flux weakening (FW) control strategy based on the reoriented dq-axis reference frame for asymmetric surface inset permanent magnet synchronous motors (ASI-PMSMs) is proposed. The ASI-PMSMs, featuring asymmetric rotors, are designed to maximize both reluctance torque and magnetic torque at the same current phase angle, thereby enhancing torque density per unit amount of the permanent magnet material. However, the ASI-PMSMs exhibit a unique characteristic where the magnet d-axis is not aligned with the reluctance d-axis, which results in a shift of their voltage limit ellipse towards the third quadrant of the dq coordinate plane. As a result, it is impossible to realize deep FW region by the conventional FW control methods since they fail to achieve the transition of dq-axis currents from the second to the third quadrant. Instead, the proposed FW control strategy reorients the dq-axis reference frame of the ASI-PMSM which can obtain the original dq-axis current command in the third quadrant, thus allowing the ASI-PMSM to operate in the deep FW region and realize the wide speed range. First, the theoretical derivation is provided, which encompasses the calculation of the flux shift angle and the mathematical modeling of the ASI-PMSM. Then the proposed FW control strategy is introduced in detail. Finally, the experimental results demonstrate the feasibility and effectiveness of the proposed FW control strategy.