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Initial Rotor Polarity Detection of Single-phase PMSM Based on Nonlinear Permeability of Permanent Magnet

This paper proposes a novel rotor polarity estimation algorithm for single-phase permanent magnet synchronous motor (SP-PMSM) with asymmetric air-gap. In general, the back-EMF or flux estimation models are used to operate the sensorless control of permanent magnet synchronous machines. However, when motor is at standstill or low speed, the back-EMF is too small to detect rotor position. Thereby, high frequency injection methods are widely used in the standstill or low speed region. In case of the SP-PMSM, when high frequency signal is injected to asymmetric air-gap single-phase PMSM motors, flux saturation phenomenon may be different unlike 3-phase machines. Due to alternating magnetic field at the air-gap, initial rotor magnetic polarity of the SP-PMSM is not easy to be estimated. As a result, the high frequency voltage signal is only injected at SP-PMSM and the current offset can be obtained by the LPF. The effectiveness and usefulness of the proposed algorithm is verified through the several experimental results.