Research On Compound Sliding Mode Variable Structure Control Method For PMSM Servo System

Permanent magnet synchronous motor plays an important role in advanced rail transit and wind power generation due to its advantages of low power consumption,small volume,simple structure and high speed regulation performance,etc.However,PMSM is a strongly coupled,multivariable and time-varying nonlinear system,moreover its performance can be influenced by unknown factors.Motor speed control system generally uses PI controller,but its very difficult to achieve a high performance of PMSM speed control system.While sliding mode variable struct are control method is employed to design controller that can improve the rapidity,stability and robustness of the whole system.This dissertation firstly outlines the vector control technique.Specifically,the id =0 is adopted to establish the mathematical model of PMSM.Secondly,the traditional SMC controller design method is introduced.The results from simulation show that the traditional sliding mode control possesses the unavoidable disadvantages,meanwhile the effectiveness of the reaching law for buffeting elimination is also be verified.The following improvements are carried out to deal with the effects of the inherent defects and unknown factors of the sliding mode control on the system:1)A sliding mode active disturbance compound current controller is designed to effectively estimate and suppress internal and external disturbances,which enhanced the system's disturbance resistance and improved the dynamic performance of the system;2)A sliding mode speed controller is designed to dynamically deal with the gain of the switching function,and adopt the adaptive variable gain approaching law with the system state,and simplify the parameters to weaken the chattering and reduce the adjustment parameters.Meanwhile instead of sign function,tanh function is used that can make the approaching law continuous;3)The load sliding mode observer is designed to combine the observation with the output of the speed controller to the current loop,in which the integral sliding surface with the observation error as the variable is used to improve the system accuracy.In order to reduce the parameter tuning complexity,the parameters are tuned to reciprocal relations,the robustness and disturbance resistance of the system are improved greatly.Finally,the simulation model of the composite control system based on observer is built.The comparison is made from load mutation,speed tracking,torque observation and internal parameter variation of the motor.The simulation results show that the compound control performance based on the observer are more effective than the traditional control method.The dynamic performance,tracking performance,anti-disturbance and robustness of the speed control system are further improved.The rationality of the algorithm is verified.