Third-Harmonic Injection for Extension of Flux-Weakening Region of Open-End Winding Interior Permanent Magnet Synchronous Motors

초록

In open-end winding (OEW) motors, zero-sequence components inevitably occur, with most of them being third harmonics. Conventional flux-weakening control methods involve the assumption of perfect cancellation of the third-harmonic components, and excessive d-axis current is injected to avoid insufficient voltage margin, which is associated with the dc-link voltage limitation in flux-weakening operation. Consequently, such control methods reduce capability and efficiency. This paper presents a novel flux-weakening control strategy for OEW motors, where the fundamental and third-harmonic components are optimized to extend the capability and improve efficiency. The optimization minimizes the RMS current while satisfying voltage, current, and torque ripple constraints, maintaining the torque linearity. For the optimization, an OEW model was constructed in multiple synchronous reference frames, and optimal references were implemented as look-up tables; moreover, a peak flux index, derived from the detected phase voltage peak and rotor speed, was defined and used to avoid insufficient voltage margin in the steady state. Simulation and experimental results showed that the proposed strategy can extend the high-speed operating region by approximately 15.7%, reduce power loss by up to 11.8%, and maintain the torque ripple within the predefined constraint. © 2015 IEEE.

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