A New Wiring Compensation System For V/v Co-phase Traction Power Supply System

As a modern transportation tool with low energy consumption,strong transport capacity,and environmental friendliness,electrified railway plays a decisive role in national life and social and economic development.Electrified railway is a kind of highpower single-phase load,which will bring power quality problems such as negative sequence,harmonics,and reactive power to the public grid during operation.Passing the neutral section is also the major issues in the electrified railways traction power supply system.Cophased tracion power supply system is a reliable solution that can comprehensively solve the problems of all above,however,the large capacity of active compensation device making it difficult to gain popularity.Therefore,it is of great economic value to find a compensation system that has small capacity of active devices without loss of compensation.The development history of electrified railways and causes of the power quality problems are introduced.The compensation methods especially the cophased tracion power supply system are summarized.Hybrid Railway Power Quality Compensator(HPQC)with small active device capacity and low transformer port voltage is selected after analyzing the topology and characteristics of various compensation devices.The principle of compensation for HPQC is studied to lay the foundation for the following research work.Then,a new wiring compensation system based on V/V transformer co-phase power supply is proposed.Different from the connection of traditional compensation device,in the topology of new compensation device,the two-port of HPQC and traction load are connected to the three output phases of the V/V transformer respectively.Based on the circuit principle analysis,the mathematical relationship between the output power of the two sides of HPQC and the traction load power is obtained under the condition of full compensation after analyzing the topology of the new wiring compensation system.As a reference,a similar analysis is performed on the conventional wiring compensation system to obtain the parameter relationships among the power of HPQC and the traction load.Comparing the output power of the two wiring compensation systems,the result shows the new wiring compensation system is more economical and more adaptable to railway development trends.Considering the fluctuating and random railway load in the actual operation,design principles of the impedance branch of the HPQC are proposed.The mathematical language is used to describe the selection of the optimal impedance branch parameters accurately,so that the converter capacity in the HPQC is minimized.According to the design principles,the optimal branch impedance values and minimum converter capacity of the HPQC under the new and traditional wiring compensation systems are determined.Comparing the converter capacity of HPQC under two wiring compensation systems under the change of traction load,it can be seen that the new wiring compensation system also has the advantages of small active device capacity.Finally,the control system of the new wiring compensation system was studied in this paper.In order to get more accurate reference signals,an improved reference signal detection method was proposed based on the instantaneous power theory.To maintain the stability of the voltage on the converters DC side,both converters are closed-loop controlled.Hysteresis control method is used to track the current signal.Simulation models were also established by Simulink,and the simulation results of two wiring compensation systems were given.