Research On Modeling And Capacity Configuration Optimization About Hybrid Energy Storage System Of Micro-grid

With the increasing capacity of micro-power in micro-grid, the issue of power quality and system stability caused by power fluctuations when micro-grid is in islanded operation has made more and more researchers pay attention to it. The problem can be solved if the energy storage system is applied to micro-grid. But there are some defects in a single storage device, and this will cause the excess energy of micro-powers cannot be used effectively. In recent years, in order to optimize the energy structure and improve grid reliability, the domestic and foreign electric power researchers have applied hybrid energy storage system which contains power-type and energy- type power to micro- grid. For popularizing hybrid energy storage system in micro- grid, this paper studies the control strategy and optimization capacity configuration of hybrid energy storage system by building micro-grid platform with photovoltaic and energy storage system in a power system simulation software-DIg SILENT. The main contents are as follows:Firstly, this article analysis the dynamic model of photovoltaic generation system, battery energy storage system, super capacitor energy storage system and electric load. Then using power business software-DIg SILENT building the above model units of micro- grid.Secondly, it introduces the structure and control strategy of hybrid energy storage system. The structure and working principle of bidirectional DC/DC converter and DC/AC inverter are introduced in detail. This paper designs a coordinated control strategy of hybrid energy storage system: in order to stabilize the DC bus voltage, it divides the inner- loop current value by using low-pass filters. The low- frequency part is used as reference value of battery and the high- frequency part is used as reference value of super capacitor. Also the simulation results show the effectiveness of this coordinated control.Thirdly, this paper used DIg SILENT to put up a simulation model of micro-grid for researching system response characteristic when the micro-powers and load are changed in grid-connected mode or islanded mode. The simulation verifies that compared to battery, super capacitor will support the power quickly if the micro- grid’s parameters are changed. And this will effectively shorten the time and volatility shocks.Finally, this paper studies the optimization capacity configuration about hybrid energy storage system. And two objective functions are established, one is to minimize the capitalized cost of hybrid energy storage system, the other one is to minimize the smoothing rate of micro-grid. In order to convert multi-objective function into single-objective function, the paper transforms the second objective function into constraints. Particle swarm optimization is used to solve the optimization problem which is put forward in this paper. The result proves the feasibility of this method.