Variable time constant filtering control for MMC-HESS considering wind power fluctuations

Wind power exhibits frequent fluctuations, which can impact the stability of the power grid. The impact of wind power on grid stability can be mitigated by using energy storage system whose battery lifespan can be extended by control strategies. This study focuses on the design of a modular multilevel hybrid energy storage system that incorporates both battery packs and supercapacitors. This system aims to effectively smooth the fluctuation of wind power and prolong the lifespan of battery packs. The power distribution between the battery packs and the supercapacitors is achieved through a first-order low-pass filter. The low-frequency power variations are smoothed using the battery packs, while the time constant of the filter is adjusted based on changes in the state of charge of battery packs. This approach prevents overcharging and overdischarging of the battery packs, thereby increasing their lifespan. The remaining high-frequency power variations are handled using the supercapacitors. Simulation results and a comparison with fixed time constant low-pass filtering demonstrate that the grid-connected power meets national standards following the implementation of the energy storage configuration. The proposed control strategy effectively allocates high- and low-frequency energy storage power, resulting in an 18.34% increase in battery pack lifespan.