Study Of The Electrically Excited Synchronous Motor Speed Control System

Electrically excited synchronous motor(EESM)has the characteristics of high order,nonlinear and strong coupling,so it is difficult to be controlled.However it has the advantages of adjustable power factor,high efficiency,high precision torque control so it is widely used in high power applications.The obtain of flux,the obtain of voltage and current and the obtain of rotor position would influence the performance of speed control system.In order to improve the performance of speed control system,this paper focused on the study of reduced-order flux observer and improvement of initial angle detection and the rotor position detection based on speed sensor control.Based on the mathematical model of EESM,the vector control system with air-gap flux oriented is studied.In this paper,the transfer function of the current loop,the speed loop,the excitation loop and the air-gap flux linkage control are deduced,and the PI controller in these links are designed.The accurate of flux observer have influence on the speed control system of EESM,the flux model of the state observer can be designed by combining the state equation of motor with the modern control theory.By using “continuous to discretization” method,the reduced-order flux observer could be discretized,which can be realized in the computer control system.The Forward Euler method and the Trapezoidal method are taken to discretize the observer.Different discretization algorithms have different effects on the stability of the motor system,the Forward Euler method is limited by the sampling time and the speed of the motor,however,the Trapezoidal method is not limited by these.In the motor,motor parameters will be affected by the factors of temperature,magnetic saturation and motor frequency,this paper analyzes the change of pole distributions of system under different parameters.The experimental results of the vector control system based on the state observer for EESM are presented.The detection of rotor position have influence on the start and the running of motor.On the part of initial angle detection,this paper study the signal injection method and use sliding discrete fourier transform(SDFT)improve the method.Compared with the traditional voltage integral method,the improved signal injection method can detect initial angle accurately and can overcome the disadvantages of integral drift faults.The initial position detection based on signal injection method is verified by experiments,and the accuracy of the method is verified.After the start of motor,rotor signal injection method is taken to detect speed and rotor position when the motor is running.Based on the analysis of no influence caused by damping winding,this paper design corresponding compensation to compensate the influence in speed control system caused by high frequency signal in rotor.The phase locked loop is designed to extract the rotor position,and the transfer function of the speed loop is analyzed and verified by simulation.Finally,the hardware platform and the software of the system are designed.In the design of the experimental platform,the main circuit,control circuit and signal detection circuit are designed.The experiment is further supplemented and the corresponding experimental waveforms are given.