Research On Control Strategy Of Hybrid Energy Storage Of Microgrid

Microgrid is a small power distribution system which is composed of one or more kinds of renewable distributed power, storage system, energy conversion device, load and protection device, microgrid can integrate and manage renewable distributed energy sources effectively, and reduce the adverse effects to the traditional grid when high permeability renewable distributed energy sources connected to power grid. Microgrid has two operation modes: grid connected state and island state. In this paper, a battery-super capacitor hybrid energy storage system(HESS) is adopted, and the control strategy of the hybrid energy storage system is studied. The control strategies of grid connected state and isolated island state are analyzed and improved to improve the economy and reliability of microgrid. The main research contents are as follows:When microgrid is in the grid connected state, bus voltage is controlled by grid, The hybrid energy storage system is responsible for stabilizing the power fluctuation of renewable distributed power, improving the quality of grid connected power, distributing power of charge and discharge power of battery and super capacitor reasonably, improving the performance and life of the energy storage system. The conventional control strategy of the PV-storage micro-grid hybrid energy storage system regard battery as an ideal element which has infinite capacity, however, the battery capacity is limited, the conventional control strategy is no longer suitable when the threshold of battery state-of-charge(SOC) is reached and can not work properly. Thus, this paper proposed a new control strategy for the PV-storage micro-grid HESS based on the second-order low-pass filtering method. This strategy takes into account of the SOC of super-capacitor and battery, adjusting the reference value of output current of energy storage element, and maintaining the SOC of storage element, the capacity requirement of battery and super capacitor is reduced and the practicability and economy of the hybrid energy storage system are improved. The overall control scheme of hybrid energy storage system was proposed and simulated in MATLAB Simulink, the results validate the correctness and feasibility of the proposed method.When microgrid is in the island state, the output power fluctuation of renewable distributed energy has great influence on the power quality and safety stability of the load terminal. Hybrid energy storage system needs to stable bus voltage and improve the reliability of micro grid to ensure the power quality of local load. This paper proposes a new battery- super capacitor hybrid energy storage system control strategy for islanding state. Improvements in the traditional hybrid control strategy on energy storage can eliminate the digital filtering. The proposed method is able to maintain a stable bus voltage without changing the control mode when the super capacitor battery reaches this limit and improves the micro-grid reliability. Small signal modeling for hybrid energy Storage System, analysis of dynamic performance. Finally, simulation and experimental studies verified the correctness and feasibility of the proposed control strategy.