Research On Negative Sequence Treatment Scheme Of Substation Group Co-phase Interconnected Traction Power Supply System

As the AC-DC-AC locomotive gradually replaces AC-DC locomotive as the main load of China railway transportation,the power quality problem of electrified railway has gradually turned into negative sequence problems,especially in areas with poor grids.The grid around the Golmud-Lhasa section of the Qinghai-Tibet Railway is poor.When the load of traction power supply system is high,the three-phase imbalance of power system must be treated,otherwise it will result in adverse effects.Meanwhile,the railway has continuous and long ramps.For ensuring the safety of locomotive power supply and railway operation,it is not appropriate to set too many electrical phase separations.Using the substation group interconnected co-phase power supply system can effectively reduce the number of phase separations,maintain power supply for locomotives uninterrupted and make the power quality meet the national standard requirements.Negative sequence treatment is one of the key technologies of the substation group interconnected scheme.The respective principles of reactive and active negative sequence control schemes are studied.The main control devices of the two schemes,static var generator(SVG)and co-phase compensation device(CPD),are analyzed.Comparing the two schemes,the reactive scheme is more suitable for the negative sequence centralized treatment of the co-phase interconnected substation group power supply system.Analyze the characteristics of the Analyze the characteristics of the traction substation group through power supply system structure and reactive scheme,the electrical quantity relationship between the ports and components in the group is derived.Their negative sequence treatment methodology is derived.To adapt to different power factor traction loads,the control scheme is divided into two-port negative sequence treatment mode and three-port negative sequence treatment mode,and the switching control strategy between modes is given.By using the phase identification method in the instantaneous reactive power theory to separate the active and reactive components of the traction load.The command current of the control system is calculated from the two components.A triangular wave modulation method is used to generate the PWM control signal for SVG controlling.According to the different treatment modes of the two negative sequence governance schemes,the specific load current detection method and SVG control method are determined.A substation group on the Qinghai-Tibet line is selected,and according to its power supply system,a negative sequence management scheme based on two matching transformers and SVG is designed.The load conditions of the substation group are set,and the two negative sequence control schemes with different loads are simulated.The simulation results prove that the reactive power negative sequence control scheme is effective,and the control strategy is feasible.It can identify the load faster and can adapt to the load fluctuations.