Decentralized Control of Multiple Supercapacitors for Hybrid Energy Storage Converter in Off-grid Mode under Power Fluctuations and Short-time High Power

Energy storage converter (ESC) has been widely used in modern power systems due to its flexible bidirectional power flow. Faced with the power outage, ESC is expected to transfer seamlessly from grid-connected mode to off-grid mode. In off-grid mode, pulsed power load and intermittent renewable generations lead to battery degradation because ESC is used to maintain AC-bus voltage. To address this challenge, the hybrid energy storage converter (HESC) composed of a battery and supercapacitor can be an effective solution. However, most existing HESCs are short of extensibility and flexibility. Besides, it cannot deal with short-time high power beyond battery capacity. In this paper, multiple supercapacitor modules are designed for off-grid applications of HESC. The power allocation strategy between battery and supercapacitors is proposed, considering the ability to handle short-time high power. Besides, power sharing among multiple supercapacitor modules and charge strategy are involved. Under the proposed scheme, the supercapacitor modules can be inserted directly into the original battery-only ESC without deploying a communication line. The high-frequency power and short-term high power will be provided by the supercapacitor. Thus, the battery can be well protected despite various power fluctuations. The proposed method is verified by simulation and experiments.