Research on control strategy of battery-supercapacitor hybrid energy storage system based on droop control[Research on improved droop control strategy to improve dynamic characteristics of DC microgrid]

The hybrid energy storage system can compensate the bus power fluctuation caused by the output power and load variation of the generator set in the Direct Current (DC) microgrid. In the current control strategy, the voltage droop method is used to control the non-high-frequency components of the battery to suppress the power fluctuation of the bus and the integral droop method is used to control the components of the supercapacitor to suppress the high-frequency power fluctuation. The effect of this strategy is similar to that of a filter, which automatically divides the ripple power into high frequency and non-high-frequency ripple components. However, when the voltage drop method is adopted, the difference of battery State of charge (SOC) in the parallel hybrid energy storage unit is not considered and the non-high-frequency fluctuation components subjected to by the battery are not redistributed, which is not beneficial to the avoidance of battery overcharge and over discharge. It is considered that the voltage drop coefficient will be affected by SOC, the voltage drop coefficient is divided by the n power of SOC to get a new voltage drop coefficient, and then the improved voltage drop method related to the voltage drop coefficient SOC is obtained, and then a new coordinated control strategy is obtained by combining the integral drop method. Simulation and experimental results show that the proposed control strategy can reallocate the non-high-frequency power according to the SOC of the battery and suppress the bus power fluctuation at the same time, so as to realize the SOC balance of different energy storage cells, and the bus voltage fluctuation is small during the whole process.