Research On Speed ​​Estimation And Decoupling In Sliding Mode Control Of Asynchronous Motor

Asynchronous motor is a nonlinear system, with characteristics of strong coupling and multivariate, and an uncertainty of load disturbance and parameter perturbation. In the control system of asynchronous motor, the external environment has a certain influence on the motor’s parameter. To ensure that the asynchronous motor is adaptable to the influence of various external disturbances and load disturbances, and having a good robustness at the same time, an improvement to the current control system is required.As an effective nonlinear control system, Sliding Mode Control, replacing the PI control, has better disturbance rejection ability towards external disturbances and parameter perturbation, besides good robustness. As a result, the application fields of asynchronous motor are expanding widely. The research works of this topic are as follows:(1)In asynchronous motor control system, since its parameters change, the estimated value of output speed cannot reach the required accuracy. Therefore, this project proposes a control strategy based on sliding mode control, and applies the improved interactive model reference adaptive system to motor speed estimation. Firstly, a kind of interactive model reference adaptive system estimation method which can identify stator resistance and rotating speed simultaneously has been designed. In regard to the complicated problems about PI gain coefficient adjustment in the estimation by using conventional model reference adaptive system, Sliding Mode Control is used to replace PI control unit, which ensures the whole system a strong robustness to the changes of the stator resistance, and improves the control precision of the whole system.(2)In the vector control system of asynchronous motor, cross coupling appears between d axis and q axis of electric current loop, leading to the coupling and delay of traditional PI controller. Therefore, this project adopts a current decoupling control method in which improved internal model control is combined with sliding mode controller. At first, immune algorithms has been combined with internal model control, so that dynamic adjustment of filtering time constant can be completed effectively. Through the above control strategy, the impacts on the dynamic characteristics of the overall system due to the constancy of the filter time constant in the process of the internal model control can be solved well. Upon the completion of the internal model control improvement, the improved internal model is then applied to the decoupling algorithm of ideal motor model. Meanwhile, sliding mode variable structure controller can improve internal model control decoupled model adjustment, and suppress perturbation of model parameter and external disturbance, making the system have good robustness during the whole operation.(3)On the basis of the improvement method about asynchronous motor listed above, build a simulation platform for verification. The simulation result showed that the designed improved interactive MRAS asynchronous motor speed sensorless system, based on sliding mode control, is able to calculate revolving speed relatively accurately, thus improving the control precision of the whole system; the designed current decoupled control method, with a combination of modified internal model control and sliding mode controller, is able to achieve dynamic decoupling effectively, thus improving the dynamic performance of asynchronous motor.