Research On Four Quadrant Converter For Electric Locomotive

Electric locomotive traction has experienced for 40 years in China,the control technology was developed to four quadrant converter(4QC)and AC drive at present from diode rectifier and DC drive in earlier.4QC because of its high power factor,grid side current has fine sinusoidal,energy feedback,high energy utilization,is gradually occupied the dominant position in the field of electric locomotive traction.In this thesis,current control technology of 4QC will be researched.This thesis analyzes the traditional theory of 4QC,including the transient mathematical model and periodic average state space model,the design method of main circuit parameters,single phase locked loop(SPLL)based on discrete fourier transform(DFT),tranditional direct current control(DCC)and indirect current control(ICC)algorithm.In order to solve the poor robustness of ICC and the weak disturbance rejection of DCC,the tranditional control algorithm need to be improved.For ICC,grid side current is decomposed by DFT,the decoupling control model of active current and reactive current to AC side voltage is obtained.And the next,design the closed-loop controller with active current and reactive current by hysteresis algorithm to achieve grid side current control algorithm.In this thesis,the simulation waveform of 500 Hz switching frequency 4QC under the start up,no load,full load,energy feedback are given.For DCC,the mixed controller,which is PI controller and repetitive controller in parallel,is adopted in current loop controller.The role of repetitive controller is to ensure the current command tracking with no static error and suppress the harmonics in grid side current,the role of PI controller makes a quick response to the step command.The design process of repetitive controller and simulation waveforms of 2kHz switching frequency 4QC with PI controller and mixed controller under the start up,no load and full load are given.The hardware and software architecture of 4QC control system are given in this thesis,and the hardware signal flow diagram and software flow chart of the control system are introduced.Then,the experiment waveforms of indirect current decoupling control based on hysteresis at 500 Hz switching frequency and mixed control in current loop at 2kHz switching frequency proved the correctness of above algorithm.