Research On Absorbing And Utilizing Technology For Regenerating Energy_ Based On Ultra-capacitor

With the development of urbanization, urban railway transit receives a wide publicity as a high density mass transport. Making good use of the braking energy generated in transit braking can realize energy conservation. According to the differences in energy process, regenerating energy absorbing modes can be divided as follows: energy-consuming mode, energy- feeding back mode, energy-storing mode. In this paper, an absorbing and utilizing technology for the brake regenerating energy in urban transit based on ultra-capacitors is researched.The ultra-capacitor array of energy storage is designed firstly. Principles and equivalent circuits are introduced; merits and drawbacks of ultra-capacitors are analyzed; an ultra-capacitor array with high voltage and large capacity can be made up in series and parallel for the drawback that the single rated voltage is low, and the array scale is designed from the points of energy and power.As the wide voltage fluctuation on the ultra-capacitors, a bi-directional DC/DC converter is needed to connect the DC power supply grid of urban transit and ultra-capacitor banks. Because the high voltage ultra-capacitor banks are difficult to fulfill and the EMI issue of DC converter consisted by high voltage IGBTs is serious, a modular construction which is composed of four modules is proposed in this paper. The four converters are connected in series on the high voltage side and independent on the ultra-capacitor side to share the high voltage and large power.As a normalization module, bi-directional DC/DC converter is a multiphase Buck/Boost topology based on the control of voltage regulating on the high voltage side and current regulating with voltage limiting on the ultra-capacitor side. The designed control scheme realizes the functions as follows: energy transfer switches freely in two directions, sequence control of the contactors turning on, soft start and off, data transmission through CAN bus. The simulation and experimental results verify the feasibility and correctness of the proposed control strategy.To make up a whole regenerating energy absorbing system, the key is the voltage balance control of the modules in-series. The necessity of balancing control is emphasized via system stability analysis. Maximum voltage tracking method as a voltage balancing control scheme is researched and then added to the single modular control scheme to form the integrated control strategy. Simulations and experiment results illustrate that the control strategy can achieve voltage balancing on the high voltage side to insure steady system working.