A hybrid energy storage system based on self-adaptive variational mode decomposition to smooth photovoltaic power fluctuation

The fluctuation and randomness of photovoltaic (PV) power generation can adversely affect the stable operation of the grid. The use of a hybrid energy storage system (HESS) can reduce the impact on the grid caused by PV power fluctuation. To improve the reliability and economy of the HESS, it is important to choose a reasonable power signal analysis method in the smoothing process. In this regard, a HESS based on self-adaptive variational mode decomposition (VMD) is proposed in this paper to smooth PV power fluctuation. This method determines the number of decomposed modes and grid-connected modes adaptively. Moreover, the VMD-Hilbert method is used to allocate the power of HESS to lead-carbon batteries and supercapacitors. In addition, a HESS economic evaluation model is developed. The results indicate that after self-adaptive VMD, the PV power fluctuation rate in different weather conditions is reduced to 9.68 %/5 min, 9.49 %/5 min, and 8.19 %/5 min respectively, which is lower than that before smoothing and meets the PV grid-connected fluctuation standard. Due to the optimization of grid-connected mode number, the power of HESS can reduce by 17.36 % on sunny days. Also, the HESS life cycle annualized cost in the maximum fluctuation weather condition reduces by 24.89 % compared to when empirical mode decomposition (EMD) is used.