Research On A Comprehensive Compensation Scheme For Co-phase Interconnected Power Supply System Based On High-voltage Traction Cable

Plateau electrified railway is an important link in the construction and planning of China’s railway network.In the plateau area,the power grid structure is weak,the power supply ability is poor,the short-circuit capacity is small,and the power quality problems dominated by reactive power and negative sequence are more prominent.At the same time,the long and large ramps are dense on the railway line,and it is easy to cause "slope stop" accidents in the process of the locomotive passing through the neutral sections.Therefore,aiming at the cophase interconnected power supply system based on high-voltage traction cable,this paper focuses on the key technologies of reactive power and negative sequence compensation,which can effectively solve the problem of power quality,improve the power supply capacity and cancels the neutral sections,so as to provide important technical support for the efficient and safe operation of plateau electrified railway.Firstly,based on the cable parameters and power supply system structure,a model of the co-phase interconnected power supply system based on high-voltage traction cable is established,and the correctness of the model is verified by theoretical calculation results,and the distribution characteristics of voltage and reactive power along the line are analyzed.The influence of different compensation methods on the governance effect of voltage and power factor is studied,the scheme of decentralized switching shunt reactors along the railway line combined with dynamic reactive power compensation in the main traction substation is proposed,the position of reactive power compensation device is determined and the reactive power compensation capacity is solved.Secondly,the mathematical model of 2-port active power type negative sequence compensation and 3-port reactive power type negative sequence compensation is established based on the co-phase power supply theory,and the impact of different wiring forms on compensation characteristics is analyzed;combined with the low-cost characteristics of passive compensation device SVC and the good dynamic performance of active compensation device SVG,a negative sequence centralized compensation scheme is proposed,which uses a new traction-compensation transformer and a hybrid reactive type compensation device.The results of the case study show that compared with the traditional scheme,the compensation device capacity in the proposed scheme is reduced by 30.8%.Finally,a three-layer control model of "compensation calculation-coordination control-current tracking" is established.In the upper control model,taking the power factor and voltage unbalance as the compensation objectives,based on the negative sequence and reactive power comprehensive compensation strategy,the compensation current calculation method is given.In the middle layer control module,the capacity allocation and the coordinated control strategy of SVC and SVG are designed;Taking the supply voltage as the constraint,the coordinated control strategy of decentralized compensation and centralized compensation is proposed.In the bottom control model,the current tracking control of SVC and SVG is used to realize the dynamic compensation effect.Taking a railway line as an example,the correctness of the comprehensive compensation scheme and the effectiveness of the hierarchical control strategy are verified by simulation.