Thrust Ripple Analysis And Suppress Of Permanent Magnet Linear Synchronous Motor

In stead of feed movement of ball screw, a permanent magnet linear synchronousmotor (PMLSM) transfers electrical energy into linear motion directly, and all intermediatetransmission mechanisms can be canceled, which has many advantages including largethrust, high dynamic response, fast acceleration and feed rate. However, thrust ripples ofPMSLM caused by load disturbances, detent force, the perturbation of system parametersand measurement noise will effect positioning accuracy and anti-interference negatively atlow speeds. Load disturbances affect control performances of PMLSM, some methods wasproposed on motor optimization and control strategy.First, the forming principle and periodic distribution of cogging force in a24-slots and22-poles PMLSM was analyzed. To investigate cogging effects, different slotshapes,varied air gap and PM width were compared by finite element method (FEM).Analysis results show that fractional slot is the most effective way to reduce the coggingforce.Second, the method combining mathematical analysis with FEM was proposed toreduce the detent force generated by end-effect, analysis results show that optimizing thelength and end structure of the mover can effectively reduce end-effect force.Third, the whole FEM model was built to analyze detent force generated by bothslot-effect and end-effect. The analysis method of combining genetic algorithm(GA) andFEM was used to optimize detent force. Simulation results show that the detent force isreduced effectively without deteriorating electromagnetic thrust.Finally, to further suppress the thrust disturbance caused by detent force and systemmeasurement noise, a method of combining kalman-filter with disturbance observer wasadopted to solve this problem. Disturbance observer observed changes of load force in realtime, in which the disturbance was equivalent to corresponding current inputs to the system.kalman-filter improves system control precision and robustness by estimating the positionand speed of mover accurately. Simulation results show that the proposed control strategyis effective.