| In order to deal with the reduction of fossil fuels and environmental pollution,the DC microgrid composed of distributed power,energy storage systems and loads has been extensively studied due to its unique advantages.In order to solve the problem of randomness and volatility of distributed power in distributed DC microgrid,the hybrid energy storage system(HESS)suppresses power fluctuations according to its own characteristics,which can make the microgrid operate stably.As the scale of microgrids becomes larger and larger,multiple HESS can meet the operation requirements of larger-capacity microgrids.Therefore,this paper mainly studies the HESS in the DC microgrid,and aims at coordinated control strategy in off-grid and grid-connected operation of microgrid in multiple HESS and between different groups,The following researches have been carried out:First,the DC microgrid model consisting of HESS,photovoltaic systems,wind turbine systems and loads has been established.Focus on the frequency division control of hybrid energy storage,allowing the supercapacitor and battery to respond to high-frequency power fluctuations and low-frequency power fluctuations respectively;establish models of photovoltaic systems and wind turbine systems,and perform different operating conditions of the microgrid based on voltage classification,which makes each unit switch under different control modes.Secondly,research on multiple hybrid energy storage in off-grid state.In order to deal with the problems of voltage deviation caused by traditional droop control and unbalanced state of charge between energy storage,the multiple hybrid energy storage control strategy considering the state of charge is proposed in the DC microgrid.The supercapacitor can use virtual voltage sources to autonomously restore the state of charge and smooth the high-frequency components of system power fluctuations,reducing DC bus voltage fluctuations;batteries smooth the low-frequency components of the system,and use consistency algorithms to achieve consistent stateof-charge between batteries.Use the final value theorem to perform frequency domain analysis to verify its stability,and build a distributed DC microgrid model for simulation under different conditions,verifying that it can achieve coordinated control within and between hybrid energy storage,improve battery performance,and make the system robust longevity.Finally,in order to reduce the impact of the grid-connected DC microgrid on the large grid and the impact on the dispatch,considering the fluctuations caused by the predicted power error,the multiple hybrid energy storage grouping control strategy is proposed.First,obtain the forecast error fluctuation in the microgrid through the BP neural network.Use wavelet packet decomposition for spectrum analysis and power distribution.The supercapacitor group responds to high-frequency power components,and the battery components are charging and discharging groups in response to low-frequency fluctuations.Each group of batteries distributes power according to the state of charge,and can switches the charging and discharging state at the same time to reduce the number of charging and discharging.The calculation example verifies that the control strategy reduces the fluctuation of the gridconnected power. |
