Research On Power Quality Control And Energy Utilization Of High Speed Trains Under Regenerative Braking Conditions

With the shift of the focus of high-speed railway construction to the western region of China,there are multiple long-distance steep downhills whose slopes are more than 20‰ or even 30‰ in the constructions of some high-speed railways.Considering that there is no clear regulation on the speed limit on the long-distance steep downhill for EMU,it is important to study the speed limit and operation mode of the EMU on long-distance steep downhill.Long duration and large braking force of continuous regenerative braking are the characteristics of EMU when it is driving through long-distance steep downhill sections.It is the reason that more energy from regenerative braking feedback to the power system.The power quality problems such as harmonics and negative sequence are serious as well,during regenerative braking condition.So it is necessary to analyze and solve these issueses.It is used for storing regenerative braking energy by both railway power conditioner(RPC)and energy storage medium.Based on the above,it is important to take advantage of regenerative braking energy and solving power quality problems synthetically.This article aimed at CRH5 EMU research the braking strategy and electrical characteristics when passing through long-distance steep downhill sections.Based on a novel RPC(SC_RPC)consisting of RPC and supercapacitor energy storage system(SC_ESS),coordinated control strategy of energy management and power quality control for high-speed railway is studyed.Meanwhile,the capacity allocation method of energy storage medium is presented.The main work of this dissertation includes three aspects:(1)This paper firstly discusses the operation mode of EMU as passing through the long-distance steep downhill sections in current researches.The methods of using regenerative braking energy and the mothods analyzing as well as controlling the power quality of high-speed railways for current research status are summarized.This paper discusses methods for studying the electrical characteristics of traction power supply systems and high speed trains.Finally the significance of this subject for this paper is expounded.(2)According to the traction power supply system principle and electrical parameter calculation,CRH5 type EMU traction drive system structure and working principle,the simulation model of traction power supply system including 6 conductor chain traction net model,traction transformer with V/x wiring and autotransformer(AT)station is established in Matlab/Simulink.At the same time,the full vehicle traction drive model of the CRH5 EMU was established in Matlab/Simulink as well.Furthermore,this paper analyzes the situation of force of EMU and the breaking system of CRH5 EMU.Finally the voltage distribution of the traction power supply system simulation model and the electrical characteristics of the EMU simulation model are analyed.(3)The operation mode and electrical characteristics of the EMU when growing up the long-distance steep downhill sections are studied in this paper.The result of the speed limit check calculation is that CRH5 EMU needs a speed limit when it go through the ramps more than-27‰ based on the relationship of monitoring braking distance,occlusion zone length and train tracking interval.At the same time,it is able to drive through the ramp whose slope is not exceeding-31‰ with only regenerative braking for CRH5 EMU.When the EMU through a ramp with its slope more than-31‰,it needs air braking force extra with electro-pneumatic composite brake.The air braking force is supplemented on the axles of trailers.The periodic braking strategy(air brake—inert—air brake)when alternate air brake is utilizing on the electric locomotive.Through simulation,the regenerative braking energy fed back to the grid and the power quality problems by the electric locomotive through the long downhill are analyzed.(4)Firstly,the coordinated control strategy for high-speed railway energy management and power quality management considering supercapacitor state of charge(SOC)is presented.Furthermore the capacity allocation of supercapacitor energy storage system(SC_ESS)is researched based on proposed coordination control strategy.With the coordinated control strategy,it is able to comprehensive utilization of regenerative braking energy and treatment the power quality problems such as harmonic currents and negative sequence currents.Meanwhile,it can take into account both peak cutting and valley filling and the protection for overcharge and overdischarge of supercapacitor with the coordinated control strategy.Amid at energy storage or peak cutting,the methods of capacity allocation for SC_ESS are proposed,respectively.Then the simulation analysis of an actual measured load power curve is carried out.Moreover,the control method of SC_RPC converters a given.The control methods of two inverters in RPC are both double hysteresis current tracking control.And the control method of SC_ESS bidirectional DC/DC converter is active power control.Finally,SC_RPC is connected to the power and load simulation model built in Chapter 2 to verify the proposed coordinated control strategy and converter control method.The effectiveness of the coordinated control strategy is proved by simulation results,which utilizes regenerative braking energy,peak shaving and valley filling,harmonic and negative sequence control and other power quality problems.