Adaptive State-of-Charge Control Strategy for Hybrid Energy Storage System Based on Grid-Forming Converter

At present, Grid-Forming (GFM) control is recognized as the most promising control technology for grid-connected converters. The energy the GFM converters provide for grid frequency support is mainly sourced from energy storage (ES). Hybrid Energy Storage (HES) systems have the potential to combine the advantages of different types of ES, thereby enhancing the frequency response and inertia emulation capabilities. Nevertheless, ES may encounter State-of-Charge (SOC) limit issues in practice. This paper focuses on the control of the HES system based on GFM converter (GFM-HES). An adaptive SOC control strategy is proposed. On the one hand, closed-loop control of the Supercapacitor terminal voltage is employed to achieve fast SOC recovery. On the other hand, adaptive SOC control for the battery is adopted to prevent it from entering the overcharge and over-discharge zone. The simulation results verify the effectiveness of the proposed control strategy.