Improvement Technology Of Electric Braking Capacity For Train Traction System In The Low Speed Range

In the train traction drive system,the braking performance is directly related to the safety of train operation.With the vigorous development of high-speed railways and urban rail transit,how to make trains brake efficiently under the premise of satisfying braking deceleration and braking distance,safety and passenger comfort has become an urgent practical engineering problem to be solved.In view of a series of problems existing in the electro-pneumatic braking system,this thesis intends to give full play to the electric braking ability of the asynchronous traction motor itself and improve the electric braking performance of the traction motor to realize pure electric braking technology of the train.The braking force of electric braking comes from asynchronous traction motor.Therefore,the mathematical models of traction motor in different coordinate systems are introduced firstly.Based on the mathematical model in the synchronous rotating coordinate system,the basic principle of vector control based on rotor magnetic field orientation is analyzed,which lays the foundation for the design of the following pure electric braking scheme.There are three main types of electric braking for asynchronous traction motors:regenerative braking,plug braking and dynamic braking.The basic working principles of these three electric braking methods are analyzed firstly.Secondly,according to the relationship between torque and slip frequency under vector control,the torque output capacity of different braking modes at low speed is analyzed.The controllability of braking torque of regenerative braking when stator frequency is greater than zero and plug braking when stator frequency is less than zero is determined.Through the field orientation of indirect vector control and the flux observation of direct vector control,the realization principle and feasibility of plug braking were proved.Furthermore,a pure electric braking scheme in which regenerative braking is naturally commutated to plug braking in the low-speed range is proposed.In urban transit trains,asynchronous traction motors have gradually developed to speed sensorless control.In order to realize pure electric braking technology based on the speed sensorless control of the adaptive full-order observer(AFO),the stability of the speed estimation system under regenerative braking and plug braking conditions is analyzed firstly when AFO adopts the conventional feedback matrix and the conventional speed adaptive algorithm,and the instability problem in regenerative braking at low speed is determined.Therefore,based on routh criterion,a feedback matrix is designed to ensure the stability of regenerative braking.In addition,the observation error of stator current excitation component is introduced into the speed adaptive algorithm to ameliorate the influence caused by neglecting the observation error of flux linkage.Finally,combined with the pure electric braking scheme of natural transition from regenerative braking to plug braking,the pure electric braking technology of traction motor based on AFO speed sensorless control is realized.In traction inverter,the dead-time is long and the modulation ratio is low at low speed,therefore,the dead-time effect is particularly significant.In order to realize effective dead-time compensation,the influence of dead-time on driving signal pulse is analyzed firstly.And then,the influence of dead-time effect on load voltage is quantified by average error voltage vectors.Finally,two dead-time compensation methods,average error voltage compensation method and error time compensation method,are designed to improve the electric braking performance of traction motor in the low speed range.Based on scaled-down experimental platform of asynchronous traction motor,the above methods to improve the electric braking capacity and braking performance of asynchronous traction motor are tested and verified,and the experimental results verify the correctness and effectiveness of the above methods.