Research On Negative Resistance Converter For Reducing Rail Potential

In urban rail transit system,there have been problems with rail potential and stray current for a long time.Stray current can corrode underground metals and building structures,causing economic losses.Excessive rail potential will affect the normal operation of equipments in the traction power supply system,and even endanger pessagers’ safety.To solve the rail potential and stray current issue,many methods have been developed.The fourth-rail system and the stray current collection system have been applied in the actual urban rail transit system.The additional DC Booster device and single-phase AC traction power supply system are still in the theoretical research stage.These methods require more modifications to the existing system and train,and have higher costs and complex structures,so there are limitations in controlling rail potential and stray current.Therefore,this thesis proposes a negative resistance converter traction power supply system(NRC-TPSS),and research on its working principles,control methods and other key technologies.Firstly,the negative resistance converter(NRC)is studied.Based on analysis of NRC topology and its working mode,this thesis reveals the opertation principle of NRC outputs continuously adjustable negative resistance,and proposed the key control strategy of NRC.In addition,this thesis studies the loss calculation and distribution characteristics of NRC in detail,which provides the foundation for parameters design of main circuit components.NRC-TPSS is composed of adding NRC,switch units and return cable in the conventional traction power supply system(C-TPSS).Then,based on analysis of the working principle of NRC-TPSS,this thesis proposes a single-capacitor train position detection scheme,which can correctly detect and judge the position and operating condition of the train,and control the working modes of NRC and the on-off state of switch units according to the judgment result.In addition,the models of C-TPSS and four-interval NRC-TPSS are established.When the system is directly grounded or floating,the distribution of rail potential and stray current are analyzed respectively.The effectiveness of NRC-TPSS in reducing the rail potential and stray current is verified by comparing the distribution curves.Finally,the simulation model of NRC-TPSS is built.The accuracy of the NRC output resistance is verified.The effect of NRC-TPSS in controlling rail potential and stray current is consistent with the theoretical analysis.At the same time,the effectiveness of the single-capacitor train position detection scheme is verified.Moreover,a down-scaled experimental prototype is design and built.The experimental results are consistent with the theoretical and simulation results,which verifies that NRC-TPSS has good application prospects in rail potential and stray current suppression application.