Research On Adaptability And Countermeasures Of Photovoltaic Generation System Accessing To Electrified Railway Traction Power Supply System

PV(photovoltaic)accessing to electrified railway traction power supply system is conducive to the green development of railway,promote the construction of rail transit energy Internet,promote the nearby consumption of PV energy,and broaden its commercial market without subsidies,whilch has significant social and economic benefits.However,PV is constrained by multiple factors due to the particularity of the application environment(such as phase-separated power supply,double random volatility,multi-vehicle traction/brake,etc.).And now there is still a lack of systematic and in-depth research on its operation characteristics and influence mechanism,especially on the system adaptability in different access forms,relevant power quality interaction mechanism,scheme comparison,countermeasures,etc.Based on this,this paper has carried out the following work around the above problems.(1)Firstly,the working mechanism of PV generation system and traction power supply system is briefly analyzed.Based on the modeling principle of PV,the engineering model of PV array,the maximum power point tracking control model,the power estimation model suitable for large-scale and long-time are established and verified.Based on the modeling principle of traction power supply system,the external power supply system,traction transformer,traction network and traction load are modeled and verified.(2)The three-phase access scheme of PV generation system and its adaptability are analyzed.The overall topology of the system is firstly given and its operation characteristics are analyzed theoretically.By deducing the effective combination form of the port transformer and designing the control strategy of the system,the unit simulation model of the system under the three-phase access scheme is established and the experimental platform is set up.Further,the effectiveness of the scheme is verified.Based on typical working conditions,the system adaptability is preliminarily simulated and experimentally analyzed,which mainly focuses on the problems of energy retransmission,reactive power,negative sequence and harmonic before and after PV access.Then,the existing operational problems are pointed out and the application suggestions are given.(3)Conserding the deficiency of three-phase access scheme,back-to-back access scheme and its adaptability of photovoltaic power generation system are studied.The topology of the system is firstly presented and its operation characteristics are analyzed theoretically.On the basis of previous studies,the system energy distribution method and the coordination control strategy of back-to-back converter are optimized.Further,the unit simulation model of the system under back-to-back access scheme is improved.Then,it is pointed out that the back-toback access scheme is more universal by comparing the two different access schemes.Based on this,the system adaptability under back-to-back access scheme is analyzed theoretically and simulated to reveal the interactive influence mechanism,which mainly focuses on the negative sequence,reactive power,traction network voltage stability,photovoltaic energy absorption capacity and so on after PV access.(4)Based on the back-to-back access scheme,a composite optimization control method considering the comprehensive compensation of power quality is proposed to deal with the adaptability problems,such as the inability to effectively improve the power quality,the low utilization rate of equipment capacity and the low comprehensive utilization rate of energy in the PV access process.First,the control system structure is given based on the comprehensive compensation mechanism and system operation characteristics.Then,the integrated energy allocation strategy of PV generation system,the back-to-back converter optimization compensation mathematical model with power quality index parameter constraints and other key parts are established one by one.Finally,the simulation verification and analysis are carried out from these aspects that include power flow distribution and power quality improvement effect in different scenarios.The relevant research results can further reveal and optimize the operation state of the PV generation system to ensure the safe,stable and efficient operation of the system.