| The output power of DC micro grid system,which is mainly composed of wind power and photoelectric power,has great fluctuation and uncertainty,which leads to great fluctuation of DC bus voltage.When it is incorporated into the large grid,it will cause the fluctuation of grid connected power and frequency,and affect the power quality of the grid.The energy storage devices in microgrid play a role of peak clipping and valley filling during microgrid operation,and maintain system stability.However,most of the energy storage elements in the market are single,which is difficult to meet the requirements of microgrid for power density and energy density at the same time.In this paper,a hybrid energy storage system composed of super capacitor and battery is proposed,which can suppress the fluctuation of DC bus voltage and stabilize the output power quality of the micro grid system.On the basis of establishing the topology of DC microgrid with wind power,photovoltaic and hybrid energy storage,this paper makes mathematical modeling and characteristic analysis of each component of microgrid,discusses the role of hybrid energy storage system in microgrid,and determines the topology of DC/DC converter for energy control.This paper analyzes the energy storage control of the DC micro grid connected to the grid,points out that the existing energy storage control has some problems,such as the excess of SOC and the poor power quality of the grid connected.A hybrid energy storage frequency division control based on the second-order low-pass filter is proposed,which adopts the adaptive fuzzy PI parameter adjustment control,and the state of two energy storage elements is adjusted Charge(SOC)is introduced into the frequency division control of hybrid energy storage system as a control quantity.The control strategy can greatly improve the control effect of energy storage system on grid connected power fluctuation.At the same time,due to the SOC regulation of the energy storage element,the power of the energy storage element is always controlled within a certain range to avoid overcharge and overdischarge,so that the grid connected operation of DC microgrid is more stable.In addition,the power characteristics of the hybrid energy storage system under the off grid operation of DC microgrid are analyzed.Considering that the capacity of the hybrid energy storage device can not work normally when the microgrid system is running and can not guarantee the stability of the bus voltage,an energy coordination control strategy for the off grid operation of microgrid is proposed,which combines the working characteristics of battery and super capacitor and SOC Limited,four working modes of hybrid energy storage system are designed,and the control strategies of energy storage elements under different working modes are studied.Finally,the proposed control strategy is verified by simulation.The results show that the hybrid energy storage system composed of super capacitor and battery can ensure that the DC microgrid can restrain the fluctuation of grid connected power,improve the quality of grid connected power,and control the power of energy storage elements within the limit range;the hybrid energy storage system can not Under the same working mode,the bus voltage can be maintained at a stable value to maintain the stability of the microgrid system.Figure[53]Table[4]Reference[80]... |
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