Research On Key Technologies Of Position/Speed Sensorless Control For Traction Motor In Rail Transit Vehicle

With the rapid development of rail transit in the recent years,the application of the position/speed sensorless control technology in rail transit vehicles has become a major development trend.The technology has virtues of reducing system cost and improving reliability of traction drive system.This paper focuses on the key issues of the position/speed sensorless control applied in rail transit,which include position/speed sensorless control in medium-and high-speed and zero-and low speed regions under the condition of low switching frequency,and flying start in position/speed sensorless control.The main contents are as follows:In position sensorless control of interior permanent magnet synchronous motor(IPMSM)for medium-and high-speed regions,the continue-time observers used to estimate back-EMF has the problems of discretization error and the cross-coupling effect on the estimated back-EMF under low switching frequency.In order to solve the problems,an accurate discrete-time model of IPMSM is rebuilt and a discrete-time state observer is proposed.The observer feedback gain is designed according to the zero-pole matching principle.Meanwhile,in order to improve the dynamic performance of the estimated rotor position and speed,a super-twisting sliding mode position observer is proposed based on the motion equations of IPMSM.The proposed position sensorless control strategy for medium-and high-speed regions based on the discrete-time state observer can estimate rotor position and speed accurately under low switching frequency,and has great steady state and dynamic performance.The traditional high frequency voltage injection methods for position sensorless control of IPMSM for zero-and low-speed regions is limited in application under low switching frequency.On the basis of analyzing the performance of high frequency voltage injection method affected by resistance change and injection frequency reduction,a position sensorless control strategy of IPMSM for zero-and low-speed regions based on fundamental model current injection under low switching frequency is proposed.In order to achieve independent control of the fundamental current and the injected current,a two-degree-of-freedom + vector PI current controller is proposed.The harmonic components in the estimated back-EMF are analyzed when the injection frequency is reduced,and the multiple adaptive filters based on the second-order second-order generalized integrator is proposed to eliminate back-EMF harmonics.Meanwhile,the proposed sensorless control strategy is extended from the stationary frame to the rotating frame which is easier to implement.Finally,a weighted transition strategy based on rotor position error is adopted to achieve the seamless transition from the zero-and low-speed method to the medium-and high-speed method.The reliable flying start is significant for the stable operation of rail transit vehicles.In order to implement the flying start in the IPMSM position sensorless control,a flying start control strategy based on the virtual resistance and the super-twisting sliding mode observer is proposed.By bypassing the current controller in normal vector control and introducing a virtual resistance in the stationary frame,the current can be controlled in the flying start operation.On this basis,the back-EMF are estimated by the super-twisting sliding mode observer with complex vector generalized integrator,and then the rotor position and speed information are obtained.In order to eliminate the cross-coupling effect on the estimated back-EMF in the digital realization process,the super-twisting sliding mode observer is designed based on the discrete-time model.Meanwhile,a stable discrete-time structure of complex vector generalized integrator using closed-loop transfer function-based method is proposed to guarantee the stability of control system in the discrete-time domain.Induction motor is the main traction motor for operating vehicles currently,the research on flying start in speed sensorless control of induction motor is still few.The problem of flying start in speed sensorless control of incution motor can be transformed into the tracking problem of d-axis rotor back-EMF.Based on the rotor back-EMF nonlinear system model,the problems that the stability cannot be guaranteed when the motor parameter changes and the robustness to the disturbance is weak in the flying start method based on the input-output feedback linearization are analyzed.On this basis,a flying start control strategy based on the integral sliding mode is proposed.The estimated speed can be obtained through the designed integral sliding surface and the equivalent control.The sigmoid function is used to suppress the chattering by designing boundary layer.A Lyapunov function is constructed to design the sliding coefficient to guarantee the stability of control system.The proposed method requires a short time to estimate the speed,has good dynamic performance,and has good robustness to motor parameter and disturbances.