Modelling And Electrical Characteristic Analysis On Novel Cable Traction Power Supply System

Novel cable traction power supply system(NCTPSS)pattern is one of the method to reduce(or cancel)electrical phase separation that exists in traction network,and power supply distance can be greatly extended,meanwhile,power quality problems of electrical railway can also be dealt with effectively,and the interconnection between trunk railways and urban rail lines can be eventually achieved.But step power supply scheme is adopted in NCTPSS and it makes cable traction network(CTN)structure complicated,moreover,load condition is various within system,power flow goes along every CTN link before using by train,moreover,harmonic current injected from train also needs to penetrate in two voltage level before feeding back to utility grid.In the existing researches that aims at NCTPSS,precise circuit and math calculation model is not established,and explicitly analyzing electrical characteristics of NCTPSS has promotion effect on its engineering application.In this paper,two-port network analytic theory is firstly utilized,and CTN was decomposed into three kinds of sub-network: traction cable,catenary-rail and traction transformer,transmission parameter matrix of every part in CTN is calculated according to electrical network analysis theory,then π-type circuit diagram of NCTPSS is built.Uniform NCTPSS calculation model is established according to nodal tearing method,to accurately calculate port voltage,port current and power output inside NCTPSS.Moreover,at fundamental frequency,impedance change of CTN is explored,consider traction work condition and regenerative braking condition when multiple trains operate,CTN voltage change,traction transformer current distribution and load power distribution percentage among single phase transformers are analyzed.In the end,at harmonic frequency,take the NCTPSS that contains one short section and two short sections as study target respectively,resonance problem is analyzed inside system with the help of Matlab/simulink model,the amplification phenomenon of harmonic current in cable traction network is analyzed under different conditions.The research result shows that,the established system calculation model based on port network and nodal voltage tearing method can take into account all components of cable traction network,compared with Simukink simulation results,mathematical model calculation result is accurate,and it is suitable for this step power supply system.In each short section,the traction network voltage at central position is the lowest.When multiple trains operate under different conditions in the system,the regenerative train is beneficial to ensure the traction network voltage level,and the long-distance power supply pattern significantly improves the regenerative braking energy utilization rate,regenerative braking energy utilization rate reaches 100% at specific condition.Compared with the existing traction power supply system,the larger distributed capacitance of traction cable leads to lower resonance frequency in NCTPSS,distribution of resonance points and harmonic current amplification phenomenon are more complex,and multiple frequency bands will enter the interval where resonance easily occurs.