A Novel Absolute Position Estimation Method for PMSM With Linear Magnetic Sensor

The embedded magnetic encoder (EME) is a new type of position sensing system that features low cost and a compact structure. Current research mainly focuses on improving the accuracy of electrical angle (incremental position) estimation. However, there is little research on mechanical angle (absolute position) estimation, which is critical for servo systems. This article presents a novel method for absolute position estimation by leveraging the periodic characteristics inherent in the non-ideal magnetic fields of imperfect permanent magnet synchronous motors (PMSMs). Firstly, the magnetic field of a typical PMSM, which inherently exhibits slight unavoidable rotor eccentricity and inhomogeneous magnets, is analyzed. The existence of sub-harmonics at the same frequency as the rotation frequency is identified. A novel specific harmonic extractor with gain scheduling (GSSHE) is then designed to extract the weak sub-harmonics. Unlike fixed-gain extractors, GSSHE balances rapid convergence and low total harmonic distortion (THD), enabling reliable extraction of sub-harmonics even when their amplitude is less than 2% of the fundamental wave. The absolute position zone estimation can be achieved only by utilizing these harmonics. Finally, several experiments are implemented to validate the proposed method on three different PMSM prototypes. The results prove the existence of sub-harmonics and the effectiveness of the proposed absolute position estimation method.