Research On Fault-tolerant Control Of Asymmetric Primary Permanent-magnet Linear Motor For Traction System

Compared with the ordinary permanent magnet synchronous linear motor,the primary permanent-magnet linear motor(PPMLM)puts the permanent magnet and the armature windings in the primary side,while the secondary side has no winding or permanent magnet.It inherits the characteristics of the permanent magnet synchronous linear motor with high power density,small volume,high efficiency and light weight.It also has the advantages of simple mechanical structure,low maintenance cost and so on.With the increase of urban population and the rapid expansion of urban scale,it is significant to relieve the pressure of public transport with urban rail transit.PPMLM can directly produce thrust force without the conversion from rotational motion to linear motion.Under this background,it is particularly suitable for rail transit lines where tunnel construction is difficult,sloping and susceptible to rain and snow.This thesis proposes a high-power traction system consisting of PPMLM and T-type three-level inverter,which is taken as the research object.Theoretical analysis and experiment verification are carried on in the normal state and the fault state respectively.In order to facilitate the theoretical analysis of the controlled object,the mathematical models of PPMLM in the stationary and rotating coordinate systems are respectively established.Then,a new traction system is proposed to control two PPMLMs with five-leg three-level inverter,in which two primary permanent magnet motors are connected to the shared leg.Considering the dual-motor traction system composed of five-leg three-level inverter,the combination of master-slave control and vector control is carried out to realize the distribution of Q-axis current in traction system.Because of the existence of the shared leg,a line voltage modulation strategy is proposed,which compensates given reference voltage of each phase with line voltage remaining unchanged.The line voltage modulation strategy solves the contradiction of different given voltage for two phases on the shared leg,and realizes the independent control of both motors.In addition,in order to keep the neutral point potential balance of the three-level inverter,the thesis detects each phase current in real time based on hysteresis loop control.To enhance the reliability of asymmetric PPMLM for traction system,this thesis puts forward the corresponding PWM modulation strategy and neutral point potential balance control strategy for two different open-switch faults.In addition,a complete set of fault-tolerant control strategies is proposed for open-phase fault of PPMLM.The proposed fault-tolerant operation modes include single motor operation mode,minimum copper loss mode and maximum thrust mode.The corresponding operation mode of traction system is analyzed under different working conditions.The proposed fault-tolerant control strategy of open-switch fault and open-phase fault in this paper can maintain the stable operation of the system,as well as keep the neutral point potential balance after fault occurs.At the end of the thesis,an experimental platform for the proposed traction system is developed based on DSP.Model-based design method is adopted to generate the relevant code automatically by the graphical fault-tolerant control model,which will be used for code integration.It realizes the efficient and rapid development of the control algorithm.The experiments are given to verify the validation of theoretical analysis and proposed schemes.