Improved sensorless control of permanent magnet synchronous machine based on third-harmonic back-EMF

This paper presents an improved rotor position estimator based on third harmonic back-EMF which is contained in windings irrespective of the operational mode and parameters and synchronously rotates with the fundamental components. Its integration, i.e. third harmonic flux-linkage, is a continuous sinusoidal signal with constant amplitude. Taking this continuous signal rather than zero-crossings as reference, the phase difference between the estimated and reference third harmonic flux-linkages can be derived by the proposed estimator at each sampling time, and used to compensate the estimation error in the speed calculated from the zero-crossings of third harmonic flux-linkage. Then, the rotor position can be derived from the compensated rotor speed and the accuracy of estimation can be significantly improved comparing with zero-crossing based estimation. Several experiments have been implemented on a dSPACE platform with a laboratory permanent magnet synchronous machine (PMSM), and the experimental results validate that the improved rotor position estimator based on the continuous signal of third harmonic flux-linkage can achieve accurate rotor position estimation and outstanding dynamic performance.