A Speed-sensorless Restarting And Control Strategy For PMSM With Uncertain Initial Speed

Permanent magnet synchronous motor(PMSM)has been widely paid attention to in rail transit and other electric traction fields because of its high power density,small size and high efficiency,which are superior to induction motor.In order to further reduce the volume of system,lower the manufacturing cost and increase the maintainability,the application demand for sensorless control technology in the field of electric traction is also increasing.At the same time,since the exact speed and rotor position information are necessary to start PMSMs,it is difficult to adopt sensorless control algorithm for PMSM control in the field of electric traction under the special condition of "restarting with unknown initial speed".In this paper,a new control algorithm of sensorless PMSM is proposed to track the speed and position of the sensorless PMSM with an uncertain initial speed and reduce the impact of "restart with speed" on the control system.Based on the mathematical modeling of three-phase PMSM,the speed/current double closed-loop vector control system of PMSM based on PI controller is designed.The availability of designed system is verified under MATLAB/Simulink simulation environment,then the related work lays a theoretical foundation for the realization of sensorless PMSM with speed restart control.To control sensorless PMSMs,a full-order sliding mode observer based on the stationaryα-β coordinate system is designed.The extended electromotive force(EMF)is estimated by the observer and used to calculated speed and rotor electric position,which are adopted as system feedbacks so that the closed-loop control can be achieved.Meanwhile,to restart free-running PMSMs,this article designs a restarting scheme to estimate initial speed and rotor electric position based on the zero-voltage vector.Digital filters are utilized to get fundamental frequency sinusoidal induced current.This current signal is used to calculate speed by phase-locked loop(PLL)technology.A phase compensation method is applied to offset the sinusoidal signal phase lag produced by the digital filter and the operating state of spinning PMSMs can be tracked without any motor parameter.Finally,this algorithm is combined with the designed sensorless control strategy to realize the effective starting and control of the PMSM under the speed restarting condition.The simulation experiment shows that after the introduction of the initial state observation algorithm of restarting with speed,the convergence time of speed observation is shortened from 1.7s to 0.12 s,the rate of dynamic response is increased by 22.2%,and the overcurrent and overvoltage in the dynamic response process are effectively suppressed,then the sensorless permanent magnet synchronous motor with initial speed can be started and controlled.The experiment on the PMSM towing experimental platform shows that the design of the initial state observation link can accurately identify the speed and position information of the motor under the action of inertia load dragging,and the motor can quickly follow the current instruction of the system in the control process without position sensor.The control algorithm designed in this paper has a certain reference value for the application of sensorless permanent magnet synchronous motor in the electric traction field which has the requirement of "restart with speed" working condition.