Improved detecting method for multiple rotating reference frames based harmonic control of PMSMs

Harmonic current in permanent magnet synchronous motors (PMSMs) is inevitable because of the nonlinearities of inverters and back electromotive force (EMF) harmonics. It can be used to reduce the energy loss and/or torque ripple of PMSM if well-controlled. One effective way of detecting and control harmonic current is a multiple reference frame (MRF) method. However, the detecting performance of traditional low-pass filter based detecting method of MRF deteriorates when the magnitude of fundamental current is much higher than harmonics, which is common in electric vehicles application. To suppress the fundamental current interference, a novel detecting methods are proposed in this paper by extracting the total harmonic currents before MRF transformation. The total harmonic currents is extracted by a subtracter and a fundamental current estimator utilizing the dynamic response characteristic of current control. The simulation and experimental results verify that the proposed method can improve the harmonic detecting accuracy and speed under high current excitation, and is also compatible with the MRF based harmonic control.