Sensorless control based on third harmonic back-EMF and PLL for permanent magnet synchronous machine

In this paper, sensorless control based on third harmonic back-EMF and phase-locked-loop (PLL) for permanent magnet synchronous machine (PMSM) is proposed. Due to air-gap field distribution and saturation, the third harmonic back-EMF usually presents in the stator phase back-EMF which can directly reflect the rotor position. By using PLL, the phase angle of third harmonic flux-linkage, which is integrated from third harmonic back-EMF, can be derived and applied to estimate the rotor position and to compensate the rotor position estimation error in flux observer which is sensitive to the parameters of machine and controller. The proposed strategies have been implemented on a dSPACE platform with a laboratory prototype of PMSM. The experimental results demonstrate that the estimators based on third harmonic back-EMF can achieve accurate steady-state rotor position estimation and satisfactory dynamic performance. Furthermore, the compensator based on third harmonic back-EMF also can significantly improve the performance of rotor position estimation and control robustness.