Model-Free High Sliding Mode Control for Permanent Magnet Synchronous Motor
Zhao Kaihui1, Liu Wenchang1, Liu Zhicheng1, Jia Lin2, Huang Gang2
1. College of Electrical and Information Engineering Hunan University of Technology Zhuzhou 412007 China; 2. College of Railway Transportation Hunan University of Technology Zhuzhou 412007 China
Abstract：Permanent magnet synchronous traction systems have been widely used in high-speed trains and urban rail because of the advantages of high power density, high overload capacity, and fast dynamic torque. PI control technology has become the mainstream control method for motors owing to the advantages of the simple method and easy engineering implementation. However, PMSM is susceptible to unknown disturbances, parameter perturbation, and other uncertainties under complex traction conditions, and it is difficult to suppress the disturbances using traditional PI control. The overall control performance of the motor decreases, and satisfactory control results cannot be achieved in high-performance applications. The control performance of high torque permanent magnet traction synchronous motor in urban rail transit is degraded by uncertainties. Therefore, this paper proposes a novel model-free non-singular fast terminal sliding mode control strategy for the speed loop based on an extended non-singular terminal sliding mode disturbance observer. Firstly, a novel ultra-model is established based on the mathematical model of the permanent magnet synchronous traction motor under parametric perturbation and unknown perturbations using the input and output of the speed loop. Secondly, the model-free non-singular fast terminal sliding mode controller is designed based on the novel ultra-model. Then, combined with the higher-order sliding and non-singular terminal sliding modes, a real-time observer is designed for estimating the unknown part of the novel ultra-model. Consequently, the system’s robustness is improved by the feedforward compensation of the controller, the control accuracy of the speed is improved, and the system jitter is reduced. Finally, a comprehensive comparison with PI control and model-free sliding mode control (MFSMC) by simulation and experiment is carried out. It is shown that the proposed control method has strong fault tolerance and anti-disturbance to motor perturbation and unknown disturbances. In addition, the dependence on the accurate mathematical model of the motor can be reduced. Simulation and experimental results show that compared with the PT control and MFSMC method, the speed controlled by the MFNFTSMC method is the least affected by the change of rotational inertia. The speed controlled by the PI control and MFSMC method cannot recover to the given speed when the load torque changes and the resistance and inductance parameters are perturbation. In contrast, the speed controlled by the MFNFTSMC method can accurately track the given speed quickly. Meanwhile, the A-phase current total harmonics distortions (THD) of PI control and MFSMC method under parameter perturbation are 9.31 % and 7.35 %, while the MFNFTSMC method is reduced to 4.15 %. Thus, the MFNFTSMC method has an effective suppression of current harmonics. Similarly, compared with the PI control and MFSMC method, the proposed MFNFTSMC method achieves lower torque pulsation: the torque errors of the PI control and MFSMC method are about 16 % and 12.5 %, while the proposed MFNFTSMC method is only about 7.75 %. As a result, the MFNFTSMC method effectively suppresses the current pulsation problem under parameter perturbation. The following conclusions can be drawn from the simulation and experimental analysis: (1) Combining the MFC method and NFTSM to design the model-free nonsingular fast terminal sliding mode controller, the speed, current, and torque of the motor are recovered to the given value in a short time under the parameter and unknown perturbations, and the dynamic response speed and robustness of the system are improved. (2) The designed ENTSMDO can accurately observe the unknown part of the ultra-local model in real-time and effectively suppress the current and torque ripple through the feedforward compensation of the controller, ensuring high-performance control of the motor. (3) Compared with PT control and the MFSMC method, the ENTSMDO-based MFNFTSMC method has better transient and steady-state performance and more robust anti-interference capability under motor parameter perturbation and external disturbance. It achieves fault- tolerant control of the motor under parameter perturbation.
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2023, Vol. 38 
