Research On Coordinated Control Strategy Of Autonomous DC Microgrid Based On SoC Droop Control

Today’s world is facing two major problems: environmental pollution and energy scarcity.Renewable energy power generation technology based on solar power has gradually developed and has become the main force of the energy revolution.Renewable energy has multiple advantages such as cleanness and high efficiency.It is bound to replace traditional fossil energy and become a key component of the future energy Internet.Although the advantages have emerged,it has also brought new problems.For example,although renewable energy power generation units can be connected to the traditional power grid through power electronic devices,their stability and controllability are obviously insufficient.In order to solve the above problems,the microgrid came into being.Among them,the DC microgrid has received widespread attention due to its simple structure,few conversion links,and no reactive power loss,the system operation and control technology has also become the key to ensuring the reliability of power supply of the DC microgrid.The research focuses on the operation control strategy of an independent DC microgrid.The main research contents are as follows:First,the concept and structure of the DC microgrid are sorted out,and each access unit of the DC microgrid is described in detail.Then,each access unit of the DC microgrid is described in detail,and the topology,modeling method and operating characteristics of each unit are given for the photovoltaic power generation system and energy storage system.The control strategy of photovoltaic power generation system is analyzed,including variable step size maximum power tracking control and droop control with voltage feedforward compensation.And the types,structures and working principles of DC voltage converters suitable for photovoltaic power generation units and energy storage units are respectively introduced.Secondly,the basic principle of the traditional droop control is analyzed,and its limitations are put forward.The state of charge equalization speed for multiple groups of energy storage units is slow,and large bus voltage deviations will occur in the SoC equalization process.Therefore,an improved SoC droop control strategy is proposed,which first judges the charging and discharging state of the energy storage system.And then finds the optimal droop curve according to the SoC value of each energy storage unit,reasonably distributes the load power,reduces the bus voltage deviation,and then redistributes power by determining the main energy storage unit,and dynamically adjust the droop coefficient within the allowable range to make the system quickly converge to an equilibrium state,further reduce the bus voltage deviation generated by the process,reduce the possibility of bus voltage fluctuation,and ensure the safe operation of the microgrid.According to the comparison results in the simulation process,the control strategy can ensure the rapid equilibrium of SoC,reduce the bus voltage deviation,and make the independent DC microgrid run stably.Finally,a coordinated control strategy with multiple modes is proposed for the independent operation of the optical storage DC microgrid,the DC microgrid is divided into four working modes,the algorithm can adaptively switch the working mode according to the changes of the SoC value and the bus voltage value,and realize the coordinated control of the photovoltaic power generation system and the energy storage system,and in different operating modes,corresponding control strategies for each unit are proposed.The simulation results show that the proposed control strategy can ensure the balance of the battery SoC,realize the stability of the bus voltage,and avoid the problem of voltage flicker.In short,in order to ensure the stability of the bus voltage and the balance of the battery state of charge,the control strategy of the DC microgrid is mainly studied,the improved control strategy is proposed,the simulation results before and after the improvement are compared through simulation,and the simulation results verify the effectiveness of the proposed strategy.