The Research On Control System Of Three-level Bidirectional Converter For Urban Rail Transit

In recent years,urban rail transit has been developed rapidly for advantages of less land occupation,strong carrying capacity,fast driving speed and light environmental pollution.The application of three-level bidirectional converters establishes an energy transmission channel between AC and DC power grids,which can not only realize the traction power supply,but also realize the return of braking power.Additionally,it has the reactive power compensation function,which could make up for the shortcomings of the existing urban rail power supply system,and has a broad application prospect.This paper focuses on the research of the three-level bidirectional converter for urban rail transit.From the perspectives of software control system design and hardware platform system design,the research work on voltage balance control,harmonic suppression control,and system scheme design,as well as the test and engineering verification are carried out.Aiming at the real-time control problem of three-level bidirectional converter,the system mathematical model is derived and analyzed at first,the active and reactive power decoupling control method is introduced,and the simulation model is built for verification.To solve the DC neutral point voltage imbalance issue in the three-level circuit structure,the influence of four space vectors on the neutral point voltage offset is analyzed,and an accurate control strategy with regulation factor is applied based on the detailed derivation of the implementation method of SVPWM.Effectiveness of the method is verified by simulations.Aiming at the current harmonic suppression of three-level bidirectional converter,the implementation forms of proportional-integral control and proportional-integral resonance control in a synchronous rotating coordinate system are studied.A harmonic suppression strategy based on the reduced-order generalized integrator is applied,the control parameters are designed in a discrete domain,and the simulation model is built to further illustrate its feasibility.Inspired by the concept of carrier phase shift,a carrier phase shift method based on SVPWM is proposed according to the corresponding relationship between space vector and action time.Aiming at the system scheme design of three-level bidirectional converter,the electrical interface and linkage relationship between it and the bidirectional converter system are analyzed.The parameter design methods of the filter inductor and the parameter selection calculation of the power device are studied.Refine the communication scheme of the control unit,sort out various signal interfaces,and list the basic conditions for the selection of the controller.Considering bidirectional operating conditions,the calculation methods of standby,traction and feedback threshold voltage are proposed.Plan a four-level fault protection scheme as the guiding input for the preparation of logic control software.Based on the software design and hardware design,the experimental verification and engineering application of the three-level bidirectional converter are carried out.The electrical performance tests include function tests,load tests,harmonic current measurements,power factor measurements and converter efficiency measurements,which have been carried out smoothly with excellent results.Combined with the engineering application,the bidirectional converter is fully tested,which proves the correctness and feasibility of the research points in this paper.