Research On Power Supply Capability Evaluation Method Of Traction Power Supply System Under Weak Power Supply Condition

It is one of the emphases of railway planning and construction in China’s "14th Five-Year Plan" to plan the construction of railway network in the western region with sichuan-tibet railway as a typical representative.As the power source of electric locomotive,the safe and reliable operation of traction power supply system is very important,and it is an important guarantee for high-quality railway transportation.However,electrified railways in the western region may face many difficulties.On the one hand,the western region is sparsely populated,the power grid structure is weak,and the external power supply has the characteristics of few accessible points,long transmission distance and small short-circuit capacity.On the other hand,the external geographical conditions in the western region are complicated,and the lines have the characteristics of high proportion of bridges and tunnels,long ramps and bends,etc.However,the traction power of electric locomotive has obvious impact,imbalance and nonlinearity,and various factors are superimposed on each other,which brings great challenges to the power supply capacity of traction power supply system.Therefore,considering the characteristics of weak external power supply and long ramp tunnel of electrified railways in the western region,it is of great significance to establish an accurate mathematical model to analyze and evaluate the power supply capacity of traction power supply system qualitatively and quantitatively,so as to provide reference for railway design,construction and operation.Firstly,this paper analyzes the operation characteristics of electrified railways in western region,considering the characteristics of few external power access points,long transmission distance,small short-circuit capacity,long ramps and tunnels,etc.,and establishes mathematical models from three aspects: external power supply,traction power supply system and traction load.Considering the coupling relationship between source-grid-load,a unified dynamic coupling model including external power supply-traction substation-traction gridelectric locomotive is established.Gauss-Saidel is used to calculate the dynamic power flow,and the running process of single train/multi-train is dynamically simulated to obtain the voltage and power distribution characteristics during the system running.Then,a power supply capability evaluation method for traction power supply system with weak power supply is proposed.Firstly,the security constraints of power supply capacity are analyzed.Based on the calculation results of dynamic power flow of traction power supply system,the safety evaluation indexes are defined from traction substation,traction network and electric locomotive levels.In addition,the maximum power supply capacity model of traction power supply system is established,and the optimal power flow is calculated by discrete particle swarm optimization algorithm with safety evaluation index as constraint condition.By solving the train departure interval and stop time,the maximum transmission power of the traction power supply system is obtained,and then the maximum traffic capacity that the line can meet is obtained.Finally,considering the access of distributed generation,a probabilistic evaluation method for power supply capability of traction power supply system is proposed.The probability model of wind speed and light intensity is established to reflect the randomness of distributed generation.According to the train position-time curve,the probability model of train position is established,which reflects the randomness of traction load.Based on this,the probability evaluation index of power supply capacity of traction power supply system is established from the aspects of traction network voltage,oc S carrying capacity and traction transformer capacity.Monte Carlo simulation is used to calculate the probability power flow,and the influence of distributed generation on traction power supply system’s operation characteristics is analyzed.According to the characteristics of weak external power supply,long ramps and tunnels,and high power impact load of western electrified railway,a dynamic model of traction power supply system with coupling of source,network and load is established in this paper.On this basis,a power supply capacity evaluation method of traction power supply system under weak power supply condition is proposed.Considering the problems such as weak grid architecture and single power supply mode,a probabilistic evaluation method of power supply capacity of traction power supply system considering distributed power supply access was proposed.Finally,the corresponding simulation verification is carried out.The method proposed in this paper can help the on-site personnel grasp the power supply capacity level in time,and provide scientific auxiliary decision for the design,construction and operation of electrified railways in the western region.