| The worldwide energy shortage and environmental pollution have promoted the rapid development of microgrid technology and renewable power generation represented by wind energy and solar power,however,the fluctuation and intermittence of renewable power generation will seriously affect the microgrid power quality and stability.Based on the power fluctuation characteristics and storage characteristics,HESS(hybrid energy storage system)is added to the DC microgrid in this paper in order to stabilize the renewable energy output fluctuation and maintain the stability of microgrid.Based on the distributed HESS in the DC microgrid,this paper mainly studies the bidirectional DC/DC converter topology and the power control strategy of the distributed HESS.In view of the characteristics of high voltage and large capacity of wind power generation system in DC microgrid,this paper adopts interleaved three-level bidirectional DC/DC converter to connect energy storage device with DC bus.The working process of the converter in different operation modes,the working principle of the two bridge arm staggered and the voltage control strategy of the flying capacitor are analyzed in details,The mathematical model of the converter is established by means of the state space averaging method,On this basis,the closed-loop design of the converter is completed.The power control strategy for distributed HESS is designed and analyzed in this paper.In this method,the first order filter is used to extract the high frequency component of the pulse power,which is used as the power reference of the supercapacitor energy storage module,the low frequency component is compensated by distributed battery module.In order to realize the reasonable allocation of the low frequency component of DC bus fluctuation power in the distributed battery module,this paper proposes an improved SOC-based(state of charge)droop control strategy.By establishing the functional relationship between the droop coefficient and SOC of ESU(energy storage unit),the energy storage units can make reasonable output according to their SOC values,the dynamic distribution of the load power between the paralleled energy storage modules can be realized by the adaptive adjustment of the droop coefficient,and finally the energy balance can be achieved.The current distribution strategy can overcome the influence of line impedance on the load power distribution,and realize the accurate allocation of the load power between the paralleled energy storage modules;the voltage compensation strategy can solve the problem of bus voltage drop caused by traditional droop controlstrategy,and ensure the stability of DC microgrid.Based on the theoretical research and simulation verification,the experimental platform of DESS(distributed energy storage systems)is established.The validity of the theoretical analysis and the control strategy are verified by experiments. |
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