Traditional hierarchical control of the microgrid does not consider the energy storage status\nof a distributed hybrid energy storage system. This leads to the inconsistency of the remaining\ncapacity of the energy storage system in the process of system operation, which is not conducive to\nthe safe and stable operation of the system. In this paper, an improved hierarchical control strategy is\nproposed: the first allocation layer completes the allocation between the distribution energy storage\nsystems considering the state of hybrid energy storage systems, and the second allocation layer\nrealizes the allocation within the hybrid energy storage systems based on variable time constant\nlow-pass filtering. Considering the extreme conditions of energy storage systems, the transfer current\nis introduced in the second allocation process. The SOC (stage of charge) of the supercapacitor\nis between 40% and 60%, which ensures that the supercapacitor has enough margin to respond\nto the power demand. An example of a 300 MW photovoltaic microgrid system in a certain area\nis analyzed. Compared with the traditional hierarchical control, the proposed control strategy\ncan reduce the SOC change of a hybrid energy storage system by 9% under the same conditions,\nand make the supercapacitor active after power stabilization, which is helpful to the stable operation\nof the microgrid.
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