Traction Load Modeling And Power Quality Evaluation Method Of Rail Transit Power Supply System

Since the 21 st century,the rapid development of urban rail transit in China has not only promoted urban construction,but also brought some social and economic benefits.But at the same time,the impact of metro traction load on the public power grid has also aroused great attention.Because the metro train uses DC traction in the operation process,there must be a large number of electronic devices,which results in the strong impact of Metro load and a large number of harmonics in the system.In addition,the subway is generally built in the more developed cities.Once an accident is caused to the public power grid,it may have a significant impact on the city's power supply and stability of social productivity.In order to prevent the occurrence of faults in advance,corresponding measures must be formulated through theoretical analysis,so as to reduce the harm of harmonics,voltage fluctuation and flicker to the public power grid,thus improving the power quality of urban power supply,ensuring the reliability and stability of urban power supply,and theoretically eliminating the potential harm of Metro load access to the power grid caused by accidents.Under this premise,this paper analyzes the impact of metro traction load on the public power grid after connecting to the power supply system by combining the simulation calculation with the actual operation of Lanzhou traction power supply system.First of all,the characteristics of Metro load and its influencing factors are described,and some indicators of power quality are introduced,as well as the harm caused by the inconsistent indicators.At the same time,according to the theoretical calculation of metro traction load,the parameters of load modeling are determined,and the effective data of traction calculation are obtained.The function type of fitting curve is determined by observing the change rule of data curve and analyzing it.Secondly,in order to evaluate the impact of metro traction load on power grid voltage quality,this paper proposes a probabilistic power flow calculation method to evaluate the impact of metro traction load on system voltage.In this paper,the collaborative particle swarm optimization algorithm is proposed to identify the parameters of the probabilistic model of metro traction load.Then in the process of probabilistic power flow calculation,a Quasi Monte Carlo simulation combined with semi invariant method is proposed to calculate the AC and DC power flow,and then the probability distribution of 110 kV incoming line node voltage of traction power supply system is obtained,which provides a theoretical basis for the study of the probability evaluation of traction load access on the power grid voltage quality.Finally,the feasibility of this method is proved by the simulation of the actual power supply system.Finally,in order to simplify the analysis process and get more accurate results,the discrete method is used to calculate the voltage flicker.First,nataf transform is used to deal with the load correlation,then the traction load is connected to the traction power supply system,and the voltage sequence of each node of the system is calculated through the power flow.Finally,the instantaneous flicker value is calculated by discretization method,and the voltage fluctuation value corresponding to the unit instantaneous flicker value in IEC standard is fitted again.Applying the above research method to the actual traction power supply network,the probability density function and voltage flicker value of the node voltage at the outlet are obtained.