Research On Coordinated Control Strategy Of Energy Storage Unit In DC Microgrid

In recent years,due to increasingly serious environmental problems and the depletion of traditional energy sources,countries all over the world have vigorously developed clean energy,which has promoted the gradual increase in the penetration rate of distributed renewable energy,has made the concept of microgrid attract widespread attention.The microgrid is mainly composed of distributed renewable energy,energy storage units and various converters.Due to the intermittent and random nature of distributed renewable energy,the energy storage unit can play the role of "peak shaving and valley filling",so Energy storage units have become an indispensable part of the microgrid.This paper takes the DC microgrid as the research object,and focuses on designing coordinated control algorithms for energy storage units so that the output voltage of each distributed power source is consistent,the output current is proportionally distributed,and the state of charge(SOC)of the energy storage unit is balanced.The research content includes:Introduce the structure of the multi-energy storage unit DC microgrid,carry out the principle analysis and mathematical modeling of the photovoltaic cell and the storage battery,study the output characteristics of the photovoltaic unit under different conditions,analyze the principle of the traditional droop control method and its two main Shortcomings;Aiming at the above shortcomings,fixed-time secondary control and voltage-current dual-compensation secondary control are proposed,in which fixedtime distributed secondary control is applied to the secondary control of the energy storage unit to adjust the voltage deviation and current sharing accuracy.The secondary control of voltage and current double compensation items is proposed.The current compensation item is generated by dynamically adjusting the reference value of SOC to adjust the current distribution accuracy,and the voltage compensation item is introduced to adjust the voltage deviation.Due to the particularity of the energy storage unit,if a fixed sag coefficient is used,it may cause overcharge or overdischarge of the battery,which will affect its life and cause the bus voltage to deviate from the reference value.Therefore,the SOC and the initial droop coefficient are combined to construct a new droop coefficient,so that it can be adaptively adjusted according to the real-time change of SOC to control the operating state of the energy storage unit,and a virtual impedance equalizer is introduced for the influence of the line impedance on the distribution accuracy;Use voltage deviation compensation to maintain the actual bus voltage near the reference value.A simulation model is built on the MATLAB/Simulink platform,the proposed method is verified through simulation,and the simulation analysis is compared with the traditional droop control method.The results obtained further verify the feasibility of the proposed control strategy.