Speed sensorless MPTC of linear induction motors for rail transit based on improved SMO

To address the high robustness of speed observation and model accuracy for speed sensorless model predictive control of linear induction motors (LIM) in rail transit, a model predictive thrust control (MPTC) strategy based on an improved sliding mode observer (SMO) was proposed. Through the improved SMO, the real-time performance and robustness of speed and flux linkage observation were enhanced, and the demand for model accuracy was lowered, thus realizing high performance model predictive control of the speed sensorless of LIM. A LIM dynamic model based on the dynamic end effect was established in the static coordinate system. A discrete model of model predictive thrust control was established. An observation method of flux linkage and speed based on the improved SMO was proposed. Subsequently, a speed sensorless MPTC system for LIM based on the improved SMO was designed. To enhance the estimation precision of speed and flux linkage, minimize sliding mode chattering, and accelerate the convergence speed, a switch function based on the continuous sigmod function was designed. Meanwhile, an improved variable exponential power reaching law was proposed to balance the contradiction between the rapid convergence and chattering of the system. The stability and dynamic performance of the improved SMO were analyzed, and the hardware-in-the-loop environment was built to verify the effectiveness of the algorithm. Experimental results show that the observation accuracy of the improved SMO is high. In the case of abrupt changes in secondary resistance and excitation inductance, the speed observation errors are 0.20 and 0.35 m·s^-1, both of which reduce by 1.4%. When the white noise perturbation with a variance of 0.01 is introduced, the maximum error is 0.20 m·s^-1, with an error rate of about 1.8%. Characterized by a fast convergence speed and less chattering of observation results, the observer exhibits a better anti-interference ability. Under the multi-speed domain conditions, the error is 0.075 m·s^-1, satisfying the performance requirements. The speed sensorless MPC system of LIM based on the improved SMO exhibits small steady state error, fast dynamic response, and good robustness performance.