Research On Control Strategy Of A Turntable Servo System With Low Speed And High Precision

The research object of this thesis is a turntable servo system,which contains an outer-rotor surface-mounted permanent magnet synchronous motor to accomplish servo control based on current and speed closed-loops.The main focus is to improve control accuracy and stability of the servo system at low speed(below 30°/s).However,strong nonlinear interference and uncertainty occur when the servo system is running at low speed,which includs angle error of measuring element,feedback noise of sampling,friction torque,cogging torque,electromagnetic torque and load variations.In this thesis,the above-mentioned nonlinear disturbance and uncertainty are regarded as a combined disturbance of the system,and a system controller is designed based on the active disturbance rejection control(ADRC)theory to realize real-time observation of the system combined disturbance.In addition,in order to satisfy the servo control requirements at low speed,a feedforward method is employed to compensate the disturbance influence.The main research contents are as follows:1.The interference factors of the system during low-speed operation are analyzed,including motor interference torque,quantization angle error by measurement,and feedback noise of sampling.Each mechanism and the corresponding suppression or compensation methods of these three factors are overviewed.2.Design a current controller based on PI control.Set proper proportional gain and integral gain parameters,and corrects the current loop to a stable first-order low-pass system,which helps the system avoid overshoot and oscillation and achieve higher dynamic performance.3.To solve the problem of quantization error in position signal sampling which is caused by the resolution limitation of the magnetic encoder,interpolation algorithm is used to compensate the sampling position signal,and the discrete position output of the encoder is converted into a continuous one,which improves the accuracy of position feedback.4.A speed controller based on ADRC is designed,which can not only suppress the noise of feedback speed signal,but also compensate the combined disturbance estimated by an extended state observer through feedforward method.Therefore,the impact of various nonlinear disturbances on the system is suppressed and the low-speed performance is improved.5.A low-speed turntable system based on an ADRC controller is established,where a set of control strategy is programmed and a series of hardware control circuits are implemented.Based on the platform,low-speed experiments are conducted to verify the effectiveness of the servo controller.Experimental results confirm that the control accuracy and stability at low speeds can meet the specification requirements.