| China’s development of the medium and long term railway network planning clearly indicated that China’s main trunk railway will be achieved electrification by 2020. At present,the electric railway in our country adopts the V/v traction power supply system which has structure simple and low cost. The negative sequence current of traction load is injected into the public power grid through the V/v traction transformer. At the same time, the power consumption of the hybrid electric railway which is a mixed race running AC-DC and the AC-DC-AC electric locomotive requires a lot of reactive power and reduces power factor.Therefore, the negative sequence and reactive power are the main power quality problems of V/v traction power supply system, which will affect the running safety of the public power grid, so the corresponding management must be carried out. Traditional power quality compensation device has the defects of large volume, poor dynamic performance and so on.The railway power regulator( RPC) based on back-to-back structure carry out comprehensive compensation for negative sequence and reactive power with regarding the traction substation as a whole of negative sequence and reactive power compensation. Electrical connection is established between the adjacent two power supply arm, which can balance the active current and reduce the negative sequence current, In the RPC system, the load on the adjacent two power supply can be compensated by the reactive power compensation, which can effectively reduce the influence of the traction load on the public power grid. The main work and innovation of this paper are as follows:(1) Starting from the basic principle of V/v traction power supply system, the relationship between the voltage and current vector connection mode, through the analysis of the V/v traction transformer, traction power supply system, expounds the V/v in the cause of formation of negative sequence current. This paper introduces the whole structure and basic components of RPC system, and analyzes the principle of negative sequence current and reactive power compensation in RPC system, and reveals the negative sequence and reactive compensation mechanism of RPC system.(2) The control strategy of the RPC system based on the synchronous rotating coordinate system is studied, and the current can be realized without static error control, and the active and reactive power can be controlled independently. Based on the analysis of the steady running state of RPC system and the operating conditions of the four quadrants, the fundamental frequency control model is established. In order to improve the current tracking response speed, the dual closed-loop vector control method of current inner loop and power,voltage outer loop is adopted. The PI controller is used in internal and external loop regulator,and the parameters of PI controller are calculated in detail. The design method of main circuit parameters of RPC system is introduced. In order to realize the real time compensation of negative sequence and reactive power in RPC system, a real-time detection method for active and reactive power compensation reference current is proposed.(3) The RPC system simulation model based on V/v traction power supply system is established, and the simulation parameters are designed in detail. Using resistive inductive load as the equivalent load of locomotive, the simulation analysis is carried out on the two kinds of different working conditions, which are only one phase of the load and the two phase power supply arm under the load of the power supply arm. The simulation results show that the RPC system has a great effect on the negative sequence and reactive power in V/v traction power supply system.(4) A new phase locked loop is proposed, which has good dynamic performance under non ideal grid environment. In order to realize accurate phase lock of the RPC system in the power grid environment under frequency mutation, voltage sag and harmonic pollution, a phase locked loop based on the principle of variable sampling period is presented. By adjusting the sampling time to control the output voltage phase signal, it can track the phase change in time at the frequency of mutation, and the response speed is fast. The harmonic components of the phase difference are filtered by optimized Goertzel filter, the filtering effect is good. The simulation results verify the validity of the phase locked loop. |
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