High Power DC/DC Converter For Flywheel Energy Storage System

Energy storage systems play an important role in electronic power supply in unexpected events, distributed generator and uninterruptible power supplies. Flywheel energy storage system (FESS) will be the main application of the future energy storage device for its advantages: environmental, efficiency, energy saving and clean. Although some flywheel systems product is already on the market, high-power flywheel energy storage system is still under study.High-power bi-directional DC/DC converter is key factor to solve the application problem of FESS. Modern high power DC/DC converter circuit is analyzed and non-isolated three-phase high-power bidirectional buck-boost DC/DC converter is proposed for the feature of high-power FESS. The relation-ship between input and output voltage can be find by analysis of the circuit in different time period. Thermal characteristics of high-power electronic devices and inductor parameter calculation are analyzed for application of the three phase high-power bi-directional buck-boost DC/DC converter.Current control methods of DC/DC converter including sliding mode control, predictive control and digital control which the main for high-power electronic are analyzed. The average current limited double-loop adjustment control method is proposed, which can be transform discrete control for digital control easily, and frequency domain analysis of small-signal model of buck-boost DC/DC converter verifies stability and dynamics by the bode diagram. Inter-cross conduct current sharing control for the three phase high-power bidirectional DC/DC converter is proposed.To verify the proposed three-phase high-power bidirectional buck-boost DC/DC converter and its control method, Simulation model is built in MATLAB. Firstly the bidirectional DC/DC converter and its digital control are proved correct. Secondly simulation of the high-power FESS under three working state confirm the truth of the proposed circuit and control algorithm, including states of current limit charging, constant voltage discharge and speed maintain.