Study On Key Techniques Of Energy-fed Traction Power System For Urban Mass Transit

Traction power supply system for urban mass transit is responsible for providing energy for railway vehicles. At present, the multi-pulse diode rectifier is still used in the most of the country in the world. Because it is simple, reliable, and easy to maintain. However, the energy can only be transmitted from AC to DC. So, it can not recover the extra train's regenerative braking energy, causing great waste of energy. In this dissertation, a new scheme of traction power supply system based on diode rectifiers and high-power PWM rectifiers is proposed. Which will fully use the advantages of both diode rectifiers and PWM rectifiers, making the system have not only good energy-saving effect and DC voltage stability, but also high reliability and cost-effective. The main circuit topology and key control technology will be studied in the dissertation. A great deal of simulation and experiments verify the theoretical analysis and design.Firstly, the study work has been focused on the selection and optimization of the main circuit for the PWM rectifier set. High capacity, low harmonics, modularity, and high reliability are looked upon as the object to select the main circuit topology. Because of avoiding zero-sequence circulating current, the isolated multiple topology with muti-windings transformer is selected. After that, an optimized system scheme is proposed, in which the AC inductance will be replaced by transformer leakage inductance. The Feasibility is analyzed and influence on the PWM rectifier is assessed. In addition, from the perspective of system control and harmonic cancellation, selects the viable connect-type of the transformer.Secondly, the capacity expansion technology of single converter based on device-parallel has been studied. It is divided into two levels including IGBT-parallel and IPM-parallel. First of all, the influencing factors of IGBT-parallel is analyzed, the corresponding solutions are given. Then, the capacity expansion scheme based on intelligent power module (IPM) is proposed. The problem about dynamic circulating current (DCC) is studied. Bye means of the in-depth analysis on the generating mechanism of DCC, a new suggestion that use differential mode inductance to attenuate DCC is given. Its effect is verified by simulation and experiments. Thirdly, the series and parallel control schemes for PWM rectifier set have been studied. By way of studying on the basic mathematical model and control method in the dq coordinate system, the series and parallel control schemes based on voltage source-current source model, and based on power source model are both proposed. The theoretical analysis and simulation results show that they can meet the demands of series and parallel of PWM converters.Fourthly, the coordinated control strategy aiming at PWM rectifier set and diode rectifier set have been studied in this dissertation. First of all, the output characteristic of diode rectifier is studied, as the base of coordinated control. Next, the two basic output characteristics such as voltage-stabilizing and voltage-droop are discussed. The corresponding realizing methods and feature are given. At last, the simplified model including the power station, overhead contact line, and train is built. Referring to three control objectives, three kinds of coordinated control strategies are presented. Their merits and defects are both introduced.Finally, an experimental system based on energy-fed traction power supply prototype rated 2MW is built. The experimental items include back-to-back experiment, series and parallel control strategy experiment, output characteristics experiment. The experimental waveforms and data demonstrate that the selected main circuit topology and control strategy in this dissertation are correct and feasible.