Research On Svg For Traction Power Supply System

Considering the problems existed in the electric traction power supply system of electrified railway, such as abundant negative sequence, harmonics and reactive power, a type of symmetrical compensation device is developed based on back-to-back SVG (Static Var Generator). This device can maintain active power balance between two power supply sections, compensate reactive power and harmonic power generated by traction load, solve three-phase power system load unbalanced by combining balance traction transformer. Therefore, it provides a feasible scheme of solving power quality problems in railway traction power supply system.Based on the principle of back-to-back SVG, the structure and principle of compensator is analyzed, the command current of compensation and system power relations are revealed. According to the characteristics of electrified railway traction loads and compensation objective, base on single-phase voltage source inverter (VSI), two-level four-multiple and diode neutral point clamped (NPC) three-level two-multiple main circuit of SVG are proposed and the basic electrical parameters of two kinds of main circuit structures are analyzed and calculated.The SVG control system proposed in this paper includes three levels. The compensation model selection is changed by traction loads, which determines that the device is only to compensate for reactive power or work as Active Power Filter (APF). The SVG control strategy is direct current control, which requires real-time reactive and harmonic current detection, low ripple and offset in the capacitor voltage. The base layer inverters are controlled by triangle wave modulation, including single polarity double frequency SPWM technology and carrier phase shifted SPWM technology.The designed compensation scheme is simulated by MATLAB/Simulink, using measured data of traction substations. According to the results of simulation, evaluate system power factor, three-phase voltage unbalance and current total harmonics distortion on the primary side. The simulation results illustrate the effectiveness of the compensation system design.Finally, determine the test and actual operation combining experimental platform. The control system is implemented in a digital manner using a DSP of TMS320F28335and the display platform is based on LabVIEW software. In terms of hardware, the peripheral circuit is designed. In the term of software, software modules of SVG controller are completed, including AD Sampling, software single-phase PLL, real-time reactive and harmonic current detection, Digital PID Controller with Anti-windup, PWM operation and man-machine interface dialogue.