Subway Regenerative Braking Based On Super Capacitor Energy Storage System

Considerable renewable electricity was generated when subway trains regenerative braking. Absorption and utilization this part of the regenerative braking energy is a measure of improving the energy utilization ratio at the field of urban rail transit. The measure not only save energy but also stabilize DC electric network fluctuation. With the accelerating construction of subway and the development of storage technology, the research on this aspect will become increasingly important.First of all, by the analysis of the functional requirements of the system, the structures and working mode of DC-DC converter is decided. Using dynamic analysis method, the braking energy is quantitatively calculated. Based on this, the parameters such as electric capacity of the energy storage system and the series-parallel way of supercapacitor storing array are designed. Considered the supercapacitor series-parallel storing array, some voltage equilibrium measures are introduced.In the light of the complexity nonlinear and energy coupling characteristics of the energy storage system, the thesis takes advantages of Energy Macroscopic Representation in modeling the energy coupling system to model the system. Moreover a control strategy is obtained by specific inversion rules. The energy flows of the model with EMR become much clearer, intuitive, and it establishes a foundation for the development of control strategies.Repetitive control technology is an effective method to restrain periodical ripples disturbance. In this paper, repetitive control is firstly introduced into supercapacitor energy storing system. In order to overcome the defect of repetitive controller in dynamic response, repetitive controller and PI controller are combined into a compound controller. However, a fast change of distribution coefficient induces a fast cancellation of the current in the supercapacitor and, thus, a voltage drop due to the series resistance. To avoid this phenomenon, a novel nonlinear proportion factor dynamic coordination strategy is used. This control scheme highlights a distribution criterion to distribute energy between the supercapacitor and the braking resistor. The proposed scheme is simulated in the PSIM environment, and the results indicate that the proposed scheme is effective.Finally, based on the overall structure of the supercapacitor energy storage system, the thesis introduces system’s hardware platform and software architecture. The supercapacitor energy storage system has already been tested in the subway station. Practical application proves that the system in the energy storage and stabilizing the DC network voltage is entirely effective and feasible.