Capacity allocation method for a hybrid energy storage system participating in secondary frequency regulation based on variational mode decomposition

• Optimized Hybrid Energy Storage System capacity for secondary frequency regulation. • Parameter-optimized Variational Mode Decomposition improves power allocation efficiency. • Economic model integrates lifecycle costs and frequency regulation benefits to maximize profit. • Double-layer optimization balances solution scope and computational overhead. Hybrid Energy Storage Systems (HESSs) are extensively employed to address issues related to frequency fluctuations. This paper introduces a method for configuring the capacity of a HESS engaged in the secondary frequency regulation, utilizing Variable Mode Decomposition (VMD). An economic model for a HESS, considering lifecycle costs and frequency regulation benefits, is constructed to maximize net income. The preliminary determination of the HESS allocation is based on optimizing parameters through VMD. The frequency regulation capacity and final power allocation are established by comprehensively considering the energy storage’s state of charge and rated power. Under the requirements and operational constraints, the optimal capacity configuration for the HESS is achieved. To verify the proposed method, various factors, such as different power allocation methods, modal decomposition methods, and allocation coefficients, are considered. The results indicate that the proposed method can achieve profits even under adverse conditions in the single-day scenario. The comparison with different modal decomposition methods validates the outstanding advantages of VMD and the importance of selecting appropriate allocation coefficients. Finally, in the multi-day scenario, the recommended capacity of HESS and threshold allocation frequencies for a specific region are determined, enhancing the economic efficiency of HESS for secondary frequency regulation.