Study On Power Supply Scheme Of Bidirectional Converter Device For Urban Rail

In recent years,the rapid development of urban rail in China has brought great convenience to people’s travel.At present,the power supply system of urban rail in China is mainly DC system.The power supply system generally uses the diode rectifier units to convert AC power to DC power,which has the advantages of low cost,strong overload capacity,mature technology,etc.,but there are also many problems such as regenerative braking energy treatment,large fluctuation of output voltage,reactive power compensation and so on.In order to make up for the disadvantages of the diode rectifier units,the domestic and foreign urban rail industry has successfully developed the bidirectional converter device based on IGBT,which has the advantages of bidirectional energy flow,stable DC grid voltage,adjustment of power factor,etc.,and it has become a new development direction of urban rail DC traction power supply system.This paper mainly carries out the relevant research work of the urban rail traction power supply system with the bidirectional converter device,and simulates the operation characteristics of the power supply system by studying the output characteristics and power supply simulation algorithm of it,so as to provide a strong theoretical support for its promotion and application in the future.Firstly,this paper introduces the structure of the urban rail traction power supply system,models each module and compares three different alternative schemes when the bidirectional converter device replaces the rectifier unit according to its functional positioning,and determines the"complete replacement"scheme as the main research object.Secondly,this paper studies the output characteristics of the bidirectional converter device,establishes the power supply calculation model considering the droop characteristic and puts forward the unified power supply calculation algorithm of urban rail AC and DC with the bidirectional converter device.At the same time,the power supply simulation module is developed based on the environment of Visual Studio 2010.Taking Xuzhou Metro Line 2 as an example,the effectiveness of the algorithm is verified,and the differences between the train equivalent models of constant current source and constant power source are compared.Then,the factors that affect the output characteristics of the bidirectional converter device are analyzed.The output characteristics of the device are mainly affected by its droop rateα,no-load voltage U_d0,capacity S_N and maximum output current I_dmax,S_N and I_dmax are related to its properties,whileαand U_d0 are mainly related to its operation control.Therefore,this paper mainly focuses on the analysis of theαand U_d0.By changing the value ofα,the operation of the system when the bidirectional converter device adopts constant pressure characteristic and droop characteristic are simulated,and the simulation results under different values ofαare compared mainly from the aspects of peak power of traction substation,network voltage and rail potential.Simultaneously,the influence of different values of U_d0 on the system is also analyzed.Then the selection strategy of droop rate and the recommended value range of no-load voltage are given.Finally,the operation characteristics of the system under the two schemes of the"rectifier units and the inverter feedback device"and the"bidirectional converter device"are compared.In the"bidirectional converter device"scheme,three droop rates are set for the bidirectional converter device.According to the recent driving plan,the system of the two schemes at peak time is carried out respectively,and the comparison is made mainly from four aspects:load process of traction and mixing station,traction network voltage,rail potential and economy.The results further illustrate the superiority of the bidirectional converter device,and it can provide the reference for the future development of urban rail traction power supply system.