An Improved Sliding Mode Observer-based Sensorless Control for the Three-phase PMSM with the Consideration of Stator Harmonic Compensation

Introduction: The sensorless control technology for permanent magnet synchronous motors typically employs a sliding mode observer to obtain rotor position and speed information based on the back electromotive force. This study aims to improve the inherent chattering and poor observation performance of the traditional sliding mode observer (SMO) in the rotor position estimation of the surface-- mounted permanent magnet synchronous motor. Methods: The super twisting algorithm (STA) is introduced to improve the traditional SMO, and the super twisting sliding mode observer (STA-SMO) is constructed to solve the chattering problem of the traditional SMO. According to different speeds, the sliding mode variable gain coefficient is designed, and a continuous function L(x) is introduced as a switching function to make the switching of the sliding mode surface smoother. Considering the problem of stator current distortion caused by dead zone, the harmonic suppression strategy of adaptive notch filter (ANF) based on the least mean square (LMS) algorithm is studied and combined with the STA-SMO method to construct a position sensorless control system considering current harmonic compensation. Comparative verification under different speed conditions is carried out to verify the control performance of the method studied in this study under a wide speed range. Results: Firstly, the speed information is introduced as a variable into the gain coefficient of the traditional STA-SMO, and the parameters are adjusted with speed, which solves the parameter matching problem in different speed domains of STA-SMO and effectively improves the stability of the observer. On this basis, the current harmonic compensation strategy based on LMS-ANF is introduced. According to the characteristics of the adaptive filter, the harmonic current of a specific wave can be extracted, and the acquisition current is compensated to suppress the influence of current harmonics on the estimation results of the observer, which further improves the accuracy of the observer. Discussion: The proposed STA-SMO with LMS-ANF harmonic compensation demonstrates superior performance over traditional SMO, effectively reducing chattering and improving stability across wide speed ranges. Experimental results confirm its robustness under dynamic loads and adaptability to speed transitions, with chattering reduced by 1.1%. The LMS-ANF strategy mitigates current harmonics, enhancing low-speed accuracy. While the method balances simplicity and reliability, future work could address near-zero-speed performance and computational efficiency for broader industrial applications. Conclusion: The STA-SMO + LMS-ANF proposed in this study can effectively improve the anti-interference ability of the observer, adapt to the application of a wide speed range, and have strong robustness and higher observer accuracy.