Permanent magnet synchronous linear motors (PMSLM) have the advantages of simple structure, no transmission mechanism, high power density ,etc. There are widely used in machine tools, medical equipment, and semiconductor manufacturing. Like rotating motors, PMSLM also requires sensors to achieve position feedback and speed feedback. However, existing mechanical sensors include encoders and Hall sensors, which have problems such as space occupation, high cost, and decreased reliability.In order to solve the above problems, two sensorless methods have been proposed and deeply studied: the back Electromotive Force (back-EMF) and high frequency (HF) signal injection. The HF injection method is suitable for estimating rotor position in medium- and low-speed regions and standstill conditions. According to the Type of injected signal, the HF injection method is divided into sinusoidal signal and square-wave. Compared with the sinusoidal signal injection method, the square-wave injection method increases the injection frequency to the PWM switching frequency, so the influence of resistance can be ignored. When the injection frequency is half of the PWM switching frequency, the fundamental frequency current can be removed by the difference of the two current sampling periods, thus eliminating the filter and reducing the system delay. The HF injection method uses saliency to estimate the motor position affected by the inductance. The structure of the permanent magnets (PM) will affect the inductance of the motor, and then affect the position estimation performance of the sensorless algorithm. For PMSLM, due to the particularity of inductance distribution, the impact on sensorless position estimation needs to be in-depth studied.This paper studies the relationship between the inductance and the position estimation accuracy of the HF square-wave injection sensorless algorithm for tubular permanent magnet synchronous linear motor (TPMSLM). Through the finite element simulation (FEM), the distribution law of the TPMSLM inductance with the change of the PM structure is quantitatively analyzed, and the influence of the PM structure parameters on the differential amplitude of the HF current is given. With the increase of the of permanent magnet’s length, the differential amplitude of high frequency current first increases and then decreases, so the maximum sensorless signal-to-noise ratio can be obtained at the maximum amplitude, thus improving the position estimation accuracy. Then, the HF square-wave voltage is injected into the stationary reference frame, and the frequency is half of the PWM switching frequency. The HF current differential equation is obtained without any filter, and the estimated position of the mover is extracted by a phase-locked loop (PLL).Finally, the experiment of sensorless position estimation is carried out by two prototypes with different PM structure parameters at different speeds. The mover selected by finite element analysis can significantly reduce the sensorless position estimation error in the experiment, verifying the effectiveness of the above comment. This research guides for improving the HF square-wave injection sensorless algorithm and motor structure optimization.

Optimization of Permanent Magnet Structure Parameters in Tubular Permanent Magnet Synchronous Linear Motor for HF Square-Wave Injection Sensorless Algorithm

Paper Proceedings: https://asmedigitalcollection.asme.org/IDETC-CIE/IDETC-CIE2021/volume/85369

ASME 2021 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference (IDETC/CIE2021)

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