Research On Synergistic Control Strategy Of Microgrid Hybrid Energy Storage System

The emergence of micro-grid has solved the small-scale intermittent energy(photovoltaic power& wind power) connection with power grid. Energy storage device is the intermediate link to keep balance between generation and load, also it is one of principal means for the stabilization of micro-grid system. In this thesis, the research on smoothing fluctuation of intermittent by energy storage converter and power despatching method between different storage devices are presented to smooth the fluctuation when in grid-connected mode and stabilize the miciro-grid frequency when in island mode. Meanwhile, the method will enhance the efficiency of the system, and also extend service lifetime of storage devices(especially battery).First of all, the allocation schemes of hybrid energy storage system(HESS including: BESS, battery energy storage system & SMES, superconducting magnet energy storage system) in micro-grid and storage system access schemes are presented in the thesis on the basis of compositing different characteristics of storage devices. The research content contains physical properties and operating principle of battery and superconducting magnet, also contains the comparison between two different types of DC/AC storage converters of SMES.Secondly in the thesis, mathematic models of energy storage systems are established. The VSC converter PCH model of battery and superconducting magnet and AC chopper model of superconducting magnet are established through the analysis of passivity proof of HESS and fundamental principle of PCH modeling.Thirdly, the micro-grid simulation model is established to compare three outer-loop control strategies, the limitation and application condition of different control strategies are also acknowledged. For meeting the demand of inner-loop, energy-shaping control(ES control) strategy is used to acquire better dynamic property and zero static error. During the comparison of different collocations of inner outer-loop control strategies, the final control strategy for energy storage system converter is presented: when in grid connected mode, outer-loop PQ control and inner-loop ES control strategy is used and when in island mode, outer-loop V/f control and inner-loop ES control strategy is used.Finally, a new choosing method of filter time constant for smoothing the intermittent power fluctuation has been proposed. Using fuzzy logic to design controller for dispatching power to different energy storage devices. Choosing the predicting soc(state of charge) of SMES and the error between predicting soc and initial soc of battery as two inputs of fuzzy controller to get the dispatching coefficient. The control strategy has been designed to enhance service lifetime of storage devices.