The Research On Optimized Control And Coordinated Operation For Multi Energy Storage In DC Microgrid

With the development and wide application of distributed energy,microgrid technology has attracted the attention of scholars at home and abroad.Because there are no reactive power,harmonic and other problems in DC microgrid,it is one of the important directions for the future development of microgrid.In order to ensure the stable operation of the isolated system,it is usually necessary to configure certain energy storage equipment and design corresponding control strategy.When the energy storage unit is operating,if its internal state of charge is unbalanced for a long time,it will lead to excessive charge and discharge of some energy storage units,which will cause equipment loss.Therefore,how to keep the charge balance of the energy storage unit is the current research focus of DC microgrid.Therefore,the research topic of this paper is multi energy storage optimal control and coordinated operation of DC microgrid.The main contents are as follows:1.The research status of microgrid at home and abroad as well as the related literature are analyzed and summarized.The RTDS real-time digital simulation platform is introduced,and the RTDS model of photovoltaic system and battery is established.The output characteristic of the photovoltaic array,control method and discharge characteristic of battery are analyzed.2.In order to balance the state of charge of energy storage system,droop control is usually used to share the current of each energy storage unit.Because the droop gain of traditional droop control remains unchanged,its current can not be reasonably shared,and the state of charge is difficult to achieve balance completely.In order to solve this problem,a virtual resistance regulation strategy based on the state of charge and e-index is designed to share the current reasonably,so as to achieve the state of charge balance.3.Because of the line resistance between each energy storage unit and the common bus,the current sharing of each energy storage unit will be affected.In order to solve this problem,a strategy based on micro-tuning resistance is proposed.By adding micro-tuning resistance to virtual resistance,the impact of line resistance on current sharing of each energy storage unit can be eliminated.With this strategy,the charge state of the energy storage unit can converge rapidly and realize balance.4.In order to eliminate the impact of line resistance,another control strategy based on virtual rated current is proposed.By adding the designed compensation term to the reference voltage,the current of each energy storage unit can be reasonably shared.Because droop control will cause voltage deviation,the voltage recovery term is designed to ensure the bus voltage to maintain the ideal level.In addition,the weak communication distributed communication architecture also reduces the pressure of communication.Finally,the state of charge of each energy storage unit can quickly converge and realize balance,and the voltage can also be maintained at the ideal level.