Research On Comprehensive Compensation Methods For Power Quality In Electric Traction Systems

As the national economy aorta and the critical infrastructure, the railway plays an important role in the modern comprehensive transportation system as well as in the national economic and social development. One major of the railway is electrified railway, which received a fast development now. Meanwhile we can’t neglect the impact electric traction systems provided to the power supply system.Firstly, multi-analysis on the structure, operationtheory and load characteristic of electric traction systems is conducted. Secondly, national standard and power quality monitoring data is given. Then the paper gives the conclusion that influences of electric traction systems on the power systems lies in harmonic wave, low power factor and unbalance problems. On the base, the paper introduces main compensation methods for power quality used in China’s electric traction systems, analyses the working principle and control strategy of TCR-FC one-phase Static Var Compensator (SVC), and establishes the device model under PSCAD/EMTDC. Finally, a method is given to improve the compensation effect, which also verify the result on PSCAD simulation. The paper provides a compensation method in which a single-phase APF is added to the SVC in parallel. PSCAD simulation indicates that the systems improve the treatment effect.Finally, for the district electrified railway load concentrated, this paper introduces a three-phase SVG device. Reactive power, harmonic and unbalance current can be compensated simultaneously after the improvement on instantaneous reactive power theory. Use of PID control in PWM can obtain the better compensation current tracking effect. Finally PSCAD simulations based on power quality data of traction substation from the detecting system are performed. Results verify the whole system structure, the method of current detection and control is correct and feasible and a comprehensive compensation included low power factor, harmonic wave, and unbalance on electric traction systems can be achieved.