Research On Main Circuit Of Cophase Traction Power Supply System Device

Existing single-phase traction power supply system frequency result in three-phase power system load unbalanced, reactive power and harmonic current pollution, particularly some adverse impacts on the high speed locomotive and heavy haul railway. Although some measures have been taken, the effect is limited. With the emergency of large capacity of power electronic devices and the development of modern power electronic control technology, as a key equipment of cophase traction power supply system,comprehensive power flow controller(CPFC) came into being,and problems caused by the existing railway power supply system can be solve.In corresponding to the various forms of tractions transformers that are used in the traction supply system, A brief description of traction power supply system with the YN, vd balance traction transformer is done in this paper. The structure and principle of balance transformer of CPFC is analyzed, and voltage, current and power transform relations are revealed. A variety of large-capacity converter topology and operating principle are analyzed, and advantages and disadvantages of diode neutral point clamped, flying capacitor and cascade multi-level converter topology are compared with. Combining the characteristics of electrified railway traction loads, based on two-level four-multiple voltage source converter(VSC) and diode neutral point clamped(NPC) three-level two-multiple VSC main circuit of CPFC are proposed. The basic electrical parameters of two kind of main circuit structures were analyzed and calculated, a reactive current and harmonic current diction method based on separating active current is proposed and method of reference current generation based on carrier phase and multi-carrier PWM techniques are proposed. In corresponding to the mid-point voltage unbalance of three-level inverter, A control algorithms of compared voltage difference between the two capacitors with zero to control the capacitor charging and discharging to realize neutral-point-balance is established.According to measured data of a traction substation, MATLAB/Simulink simulations about two kind of main circuits of CPFC have been done, and the results is included in the paper. The results has supported the system configuration,control strategy and parameter calculation method proposed in the paper, and two kind of main circuit are workable simultaneously.