Research On Simulation System Of Rail Potential And Stray Current In Metro Systems Based On Variable Resistance Module

In the modern metro systems,the safety problems caused by rail potential and stray current are increasingly serious.However,the control measures of the above problems are difficult to verify in actual metro systems.Therefore,the rail potential and stray current simulation systems have been widely concerned by researchers.The existing simulation systems are basically divided into three categories:multi-dimensional simulation systems(MDSSs),fixed impedance simulation systems(FISSs)and variable impedance simulation systems(VISSs).The modeling processes of MDSSs are complex and it is hard to build a general model which is suitable for most metro systems.For FISSs,only the static distribution of rail potential and stray current can be simulated.In VISSs,variable resistance modules(VRMs)are used as variable resistors to replace traditional resistors,which overcomes the shortcomings of the above two simulation systems.In the existing VISSs,unidirectional variable resistance modules(UVRMs)are used to represent rail series resistance.Therefore,the existing VISSs cannot simulate the rail potential and stray current when the train movement under different operation conditions.At the same time,due to the defects of the circuit structures of the simulation systems,the existing VISSs are not suitable for floating DC traction system and multi-interval DC traction system.In this paper,the circuit topologies and control strategies of VISSs are studied in detail.In this paper,two kinds of bidirectional variable resistance modules(BVRMs)are proposed firstly.Then the working principle,parameter design and control methods are described respectively.The equivalent output resistance of the BVRMs can be adjusted when the traction current flows bidirectionally.Therefore,the proposed BVRMs can be applied into VISSs to make them simulate the rail potential and stray current when the train movement under different operation conditions.Based on the proposed BVRMs,the equivalent model of the metro systems is constructed,which is comprised of the train,traction network,traction substation,rail series resistance and rail-to-ground resistance.Then the basic dynamic simulation system(B-DSS),multiple grounding scheme dynamic simulation system(MG-DSS)and multiple interval dynamic simulation system(MI-DSS)are proposed respectively for the grounded DC traction system,floating DC traction system and multi-interval DC traction system.Besides,the application scenarios,evolution laws,parameter selection and control strategies are analyzed in detail.All the three simulation systems use a single resistor to represent the rail-to-ground resistance.The distribution of the rail potential and stray current can be obtained directly by measuring the voltage across the resistor and current flowing through the resistor.In addition,besides the two BVRMs proposed in this paper,other VRMs are also suitable for the above three kinds of simulation systems to simulate rail potential and stray current.Finally,the software simulation models and hardware experimental devices of the two BVRMs are built.It is verified that the equivalent output resistance can be adjusted according to the reference value when the external traction current flows bidirectionally.Also,the software simulation models and hardware experimental devices of the three simulation systems are built.The rail potential and stray current when the train movement under different operation conditions were verified respectively in the grounded DC traction system,floating DC traction system and multi-interval DC traction system.The results of the software simulation and hardware experiment prove the feasibility and effectiveness of the proposed two BVRMs and three simulation systems.