Compound Sliding Mode Speed Control Of Asynchronous Motor Based On Disturbance Observe

Asynchronous motors are widely used in industrial control systems due to their simple structure,strong overload capacity and high reliability.The vector control of asynchronous use a speed-current cascade structure and a Proportional Integral(PI)algorithm to design controllers.As a linear control method,PI control has the problem of integral saturation and the system is susceptible to disturbance changes,which makes it difficult to meet system requirements.In order to solve the problems existing in the traditional PI control,a new sliding mode control algorithm is used to design the motor speed controller.At the same time,disturbance observer is used to improve the anti-interference performance of the system.A composite sliding mode speed control strategy of asynchronous motor based on disturbance observer is proposed,which effectively improves the dynamic performance and robustness of the motor.The main research content of this thesis is as follows:(1)In order to improve the speed control performance of asynchronous motor,this paper proposes a new motor control method based on model-free theory and sliding mode control.Firstly,the ultra-local model of asynchronous motor is established.Secondly,a new speed controller is designed based on sliding mode control theory.The contradiction between system chattering and sliding mode approximation speed is solved by introducing state variables into the traditional sliding mode constant speed approach law.Then,an extended state observer is designed to estimate the system disturbance,which further improves the system robustness.(2)Although the model-free sliding mode control with new reaching law can improve the dynamic performance and anti-interference performance of the system,the controller has a speed current cascade structure,which has many control links and complex parameter adjustment problems.In order to simplify the controller structure and improve the speed tracking performance of asynchronous motor,a model-free fractional-order sliding mode control algorithm based on nonlinear disturbance observer is proposed.Firstly,a ultra-local model of asynchronous motors under parameter perturbations is established.Secondly,in order to reduce sliding mode control chattering and improve dynamic performance,a model-free fractional sliding mode controller is established based on fractional-order theory.Then,considering that the traditional sliding mode control is robust to the matched term disturbance and insensitive to the unmatched term disturbance,the nonlinear disturbance observer is used to estimate the system disturbance and the estimated value is used in the designed sliding mode surface to improve the tracking accuracy of the system.(3)The model-free fractional-order sliding mode control algorithm shows good robustness and dynamic performance in the experiment,but this way can only ensure the global asymptotic stability of the system.In order to make the system state converge quickly in finite time,a hybrid control method with fixed-time sliding mode control and disturbance observer is designed.Firstly,a simple continuous time model for asynchronous motors is established.Then,based on the fixed-time sliding mode theory,the controller parameters are designed while proving the fixed convergence time characteristics of the controller.Finally,by designing a disturbance estimator to estimate and compensate for disturbances,the system robustness is further improved.Finally,the above three control strategies are applied to the asynchronous motor experimental platform.Compared with PI and traditional sliding mode control,the new reaching law sliding mode control effectively improves the rapidity and anti-interference of the system;Through the comparison experiment of model-free integer-order sliding mode control methods,the results show that fractional-order sliding mode control not only suppresses speed fluctuations,but also has good dynamic performance and robustness;Compared with the previous two methods,the fixed time Sliding mode control method can maintain good dynamic performance and anti-interference ability under different operating conditions.