Sensorless Position Estimation for Permanent Magnet Synchronous Linear Motor With Variable Coupling Length

Affected by the structure size of a permanent magnet synchronous linear motor, the coupling length of the mover and stator will change when the relative motion occurs. This paper analyzes the influence of the linear motor coupling length change on the position estimation accuracy of the position sensorless algorithm and proposes a Gauss-Newton iterative method to estimate the position. Compared with the existing high-frequency injection method, the proposed method is unaffected by the change of the coupling length, has strong robustness to the change of inductance parameters, and can obtain high position accuracy in the entire motion stroke. In this paper, the finite element method is used to analyze the variation law of the inductance parameter caused by the change of the coupling length, and the influence of the change of the inductance parameter on the position estimation accuracy of the position sensorless algorithm. The high-frequency differential current is obtained by the stationary reference frame high-frequency square-waveform injection method and difference processing, Moreover, the fast Fourier transform in the position domain is carried out to obtain the high-frequency differential current model function. The Gauss-Newton iterative method is used to obtain the estimated position of the linear motor in the entire motion stroke by estimating the position of each position sampling point. Lastly, the position accuracy of the proposed method and the traditional phase-locked loop method is compared and verified through experiments, and the corresponding conclusions are drawn.