Research On Sensorless Control Of High Power Traction Motors At Low Switching Frequency

The traction drive system of high-speed railways is more and more important in transportation.Permanent magnet synchronous motors are gradually replacing asynchronous motors as new directions for the development due to their small size,small moment of inertia,large low-speed output torque,and good field weakening performance.Traction motor control system has the characteristics of high power,high voltage and large current,which brings a series of problems for motor control.This paper studies and analyzes the sensorless control method in the full-speed operation range of the traction motor.First,this paper proposes a new position estimation algorithm.Based on the voltage equation in the two-phase stationary coordinate system of the IPMSM,an optimization function is constructed of which the minimum value is solved to obtain the estimated values of the motor position and speed.The convergence of the optimization function at initial position estaimation and the full speed range have been proved.The quasi-Newton method is selected as the solving algorithm.In order to ensure the convergence of the algorithm at the the positioning step and the start of the motor and,a voltage signal needs to be injected.Secondly,a new modulation method has been proposed.This method selects an even number of carrier cycles as the new switching cycle.Half of the carriers adopt the down counting and the other half of the carriers adopt the up counting to keep the output waveform center symmetrical.The duty is set from the center,and then the duty is set symmetrically to both sides in turn.The switching frequency function has been designed.This method can not only adjust the switching frequency according to the current while not change the carrier frequency,but also can maintain the high calculation frequency when the switching frequency is low.Thirdly,in order to solve the problem of large errors in the simple discretization model of the IPMSM voltage equation at low switching frequencies,an accurate discretized voltage model of IPMSM is derived after considering sampling and inverter voltage latching.The current loop controller is designed based on the precise discretization model.Since it is difficult to calculate each element of the controller matrix in real time,a table is formed by offline calculation.Finally,an IPMSM experimental platform is built.Three proposed methods are experimentally verified through experiments,which proves the rationality and correctness of the proposed method.