Research On Railway Power Flow Controller Based On Power Factor At Network Side

The fast-developing electrified railway transportation system plays an increasingly important role in national infrastructure construction and social transportation services.It has promoted the development of the national economy and providing convenient travel,and also brought out the power quality problems affecting the safe,stable and efficient operation of public power grid and traction network.The special performance of the railway power flow controller in improving the power quality problem of the traction power supply system has great potential in engineering application.In this paper,the influence of compensation power of the power flow controller on the power factor of the network is taken as the research object,and the working principle and mathematical model are analyzed in depth,and the problems of capacity saving rate,voltage unbalance,voltage fluctuation of power supply arm port and device loss are systematically studied.First of all,this paper introduces several common schemes and performance characteristics of power quality control of traction power supply system at home and abroad.Combining with the development history of domestic and foreign railway power flow controllers,the basic working principle of power flow controllers is briefly described.The application scope and the efficiency of capacity optimization measures are summarized from two aspects of control algorithm optimization and topological structure optimization.Secondly,by comparing the wiring forms of several traction transformers commonly used in traction power supply system with the vol tage phasor diagrams of high and low voltage side,the calculation method of conventional compensation power and its disadvantages are given.Combined with the formula definition of three-phase power factor on the network side and the evaluation criteria o f power supply department for the power users,mathematical model of compensating power and power factor on grid sides of the power flow controller and algebraic expression of current unbalance are presented innovatively,witch can be applicable to any type of wiring traction transformer.Through the mathematical model,the reactive and negative sequence effects after compensation can be quantified,and the physical meaning is clear and unambiguous.The margin of grid-connected points for the two evaluation criteria can reduce the compensation power and capacity requirements.Then,according to the distribution law of the measured load data,the phase angle of three-phase current phasor after the compensation is taken as the entry point.Based on the YNvd balance transformer,the surface diagrams of the railway power flow controller's design capacity and different combinations of three-phase power factor angle are drawn,and the optimal compensation mode composed of the lowest surface is designed.The compensation power distribution scheme is assessed by the actual locomotive load data,and the performance of the system is analyzed.The validity of the optimal compensation mode is verified by probability and statistics method,and the guiding statistical data of the scheme in determining the capacity of passive devices to participate in hybrid power quality control are given.At the same time,the detection method for single-phase load power and the control scheme of single-phase converter are introduced.Finally,an experimental prototype of the traction power supply system based on YNvd balance transformer and 2×5kW railway power flow controller is designed and built.The circuit topology,component parameters,control parameters and operation scheme of simulated locomotive load are introduced in detail.The compensation effects of the three common locomotive loads using the optimal compensation mode are analyzed detailedly,which verifies the theoretical correctness of the scheme proposed in this paper.The prototype provides an important reference for the popularization and application of high-power railway power flow controller in engineering and the debugging method,and it also shows the practical engineering application value of the power distribution sche me proposed in this paper.