Improved Sensorless Control of Permanent-Magnet Synchronous Machine Based on Third-Harmonic Back EMF

This paper presents an improved rotor position estimator based on a third-harmonic flux linkage which is the integration of third-harmonic back electromotive force. Different from the conventional rotor position estimation based on zero crossings of a third-harmonic flux linkage, the continuous signal is taken as reference, and the phase difference between the estimated and reference third-harmonic flux linkages is derived and used to compensate the estimation error in the speed calculated from the zero crossings at each sampling instant. Then, the rotor position can be derived from the compensated rotor speed, and the accuracy of rotor position estimation can be significantly improved, particularly under a dynamic condition. Several experiments have been implemented on a dSPACE platform with a laboratory permanent-magnet synchronous machine, 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.