Research On Fault Diagnosis And Fault Tolerant Control Of Position Sensor In Servo

Servo systems are widely used in mechanical lathes,intelligent robots,and other fields,because of their advantages of wide speed range and high control reliability.Permanent magnet synchronous motors are the most promising motors at present.In the PMSM servo system,the accuracy of rotor position affects the precise control of the speed.However,because of the external disturbances,loose internal parts and other reasons,the position sensor may be malfunctioning,or even cause the servo system to crash in severe cases.This thesis researches the fault diagnosis and fault-tolerant control method for the position sensor fault of the PMSM servo system.The concrete work is as follows:Firstly,this thesis introduces the mathematical model of PMSM and two typical faults of position sensors in servo systems.Then,building the failure model of the position sensor and simulating the model.The simulation results show that the fault of position sensor will affect the decoupling of current and cause the motor torque oscillation.The position sensor failure model in the servo system lays the foundation for the follow research.Secondly,for the jitter of the classical sliding mode control,designing a super-twisting second order sliding mode observer to determine the position and speed of the rotor.The residual error generated by the detection value and observation is used as the judgment basis for fault diagnosis.Then,verifying the fault detection scheme through Simulink.The results show that the fault detection scheme can detect faults and distinguish the types of faults validly and rapidly.Comparing with the traditional sliding mode observer,the second order sliding mode observer has higher position estimation accuracy and better chattering suppression effect.Thirdly,for the impact problem at the conversion of PMSM servo system and the sensorless control system,a fault-tolerant control method is proposed based on weight function switching control.Considering the false detection caused by external disturbance and fixed threshold,the time analysis method is designed.By comparing the fault time and the fault detection time,the false detection can be reduced.Meanwhile,an improved weight function switching strategy is designed to convert the system to the sensorless control system.The fault-tolerant control algorithm is verified on Simulink.The results show that the improved weight function switching strategy can overcome the impact.After detecting the fault of the position sensor,the system can complete a smooth transition and realize the fault-tolerant control rapidly.Finally,the fault diagnosis and fault-tolerant control method is verified on the experimental platform of PMSM servo system.The experimental results show that the proposed method can complete the fault diagnosis and fault-tolerant control of the position sensor in the PMSM servo system.The proposed fault diagnosis and fault-tolerant control method is valid and feasible.