The Research Of Electrical-magnetic Hybrid Power Quality Compensation System For Co-phase Railway Traction Supply System

With the development of electrical railway, the power quality problem caused by it draws more and more attentions. As a kind of single-phase rectifyed load, locomotives lead to negative sequence current, harmonics and reactive power. These power quality problems will seriously threat the safety operation of generation, transmission and distribution of the public grid. Hence, it’s necessary to make a sound research into the compensation methods for electrical railway to enhance the stability of the traction power supply system.The traditional compensation methods are discussed based on the analysis of the power quality problem. Reactive compensation methods are cost lowly but with an unsatisfied compensation performance. Active compensation methods could achieve good compensation performance but with a high compensation capacity as well as initial cost. Three hybrid compensation methods are proposed in this thesis. The main work and innovations of this thesis are as follows.(1) To solve power quality problem in V/V traction power supply system, a novel electrical-magnetic hybrid power quality compensation system based on railway power conditioner (RPC) and magnetic static var compensator (MSVC) is proposed in this paper. The RPC is only used to transfer active power and suppressing harmonics. The MSVC is used to compensate reactive power and suppress 3rd and 5th harmonic currents. The proposed hybrid compensation system will reduce the capacity as well as the DC link voltage of RPC. The principle of negative, reactive and harmonic currents compensation is analyzed firstly. Secondly, compensation capacity is optimized based on a certain unbalance tolerance. And then, a collaborative control strategy is proposed to make the compensation system have a fast respond speed. Furthermore, the resonant characteristic of the system is analyzed to confirm the stability of the compensation system. At last the simulation and experiment results verified the proposed structure and control strategy effectively.(2) To reduce the active compensation capacity of RPC, hybrid power quality compensator (HPQC) is proposed. HPQC could reduce the active compensation capacity by connecting inductor branch and inductor-capacitor branch into the converter, respectively. To solve the power quality problem in V/V co-phase railway power supply system, a hybrid electrical magnetic power quality compensator (HEMPQC) based on magnetic static var compensator (MSVC) and HPQC is proposed in this paper. Compared with conventional HPQC, the proposed HEMPQC could keep the active compensation capacity minimum to any load condition. The output current of MSVC is conducted to make the active compensation capacity minimum. The coupling branch impedance optimum design procedures are deduced. Based on the instantaneous current detecting and reactive current distribution method, the collaboration control strategy is proposed for HEMPQC to achieve the dynamic tracking of the reference signals. Finally, simulation and experiment results have verified the proposed hybrid compensation system and compensation method effectively.(3) Traditional hybrid power quality compensator (HPQC) could reduce the compensation capacity by the inductor-capacitor (LC) branch and inductor (L) branch of the converters. But HPQC could only work under a special working condition. A kind of improved HPQC is proposed in this paper besides HEMPQC. The fixed LC branch and L branch in conventional HPQC are changed to thyristor switch branches to adjust the branch impedance dynamically. The compensation principle is analyzed firstly and the parameters calculations are deduced. A control system is proposed. The simulation and experiment results verified the proposed improved HPQC could reduce the compensation capacit to the conventional HPQC.(4) The parameter design for back-to-back converters is proposed, including the step-down transformer design, coupling branch design and dc capacitor design. The experiment platform used in this paper is introduced. The main circuit is discussed. The control system circuit is analyzed as well as the control system software design.The advantage and disadvantage of the three proposed methodsare analyzed. The application situation is also proposed for the industry applications.