Research On Servo Fault Tolerance Control Under Position Sensor Failure

High-performance servo-speed control system based on permanent magnet synchronous motor requires to know the rotational position and speed information of the rotor real-time and accurately. It is usually obtained by means of a mechanical position sensor mounted on the rotor of the motor. However, due to the complexity of the environment, the limitation of service life and other reasons, it is easy to cause the position sensor failure. The occurrence of this kind of fault will seriously affect the control performance and even personal safety. Therefore, it is urgent to study the fault tolerant control of the servo speed control system under the position sensor fault.Firstly, this paper introduces the development of PMSM in the servo system, and analyzes the current situation of the fault tolerance of the position sensor and the sensorless development. Then, according to the mathematical model of PMSM and the characteristics of the rotor structure, the principle of vector control is discussed, and the realization principle of the space vector pulse width modulation algorithm is discussed based on the basic switch state of the inverter.Secondly, the traditional sliding mode observer is built on the basis of analyzing the robustness of sliding mode variable structure.However, considering the existence of a large number of chattering and harmonics in the conventional sliding mode observer and the reliability of fault tolerance, an adaptive synchronization filter and adaptive two order filter combined with orthogonal phase locked loop respectively for improved sliding mode observer is proposed in this paper on the motor rotor position and speed estimation. Then, the improved sliding mode observer and the traditional sliding mode observer are simulated by step tracking on the Simulink simulation platform. The simulation results show that the improved sliding mode observer has high tracking accuracy and little chattering.Then, based on the error of motor speed tracking, a method of segmentation threshold is proposed to improve the reliability of fault detection of servo speed control system. At the same time, considering the problem of large torque ripple in the switch between the sensor mode and the sensorless mode when the position sensor fault occurs and the fault recovery occurs, a compensation method is proposed in this paper. Then,the fault-tolerant control of servo-speed control system is studied on Simulink simulation platform, and the results show that the compensation scheme effectively suppresses the torque ripple between the different mode switches.Finally, the experimental platform of a 1.5kW PMSM servo speed control system based on dSPACE is implemented. And two kinds of sliding mode observer tracking performance experiment and fault tolerant control experiment under position sensor fault are analyzed on the semi-physical simulation platform. The effectiveness of the proposed fault-tolerant control scheme is verified by experiments.