Bidirectional Power Control Strategy for Super Capacitor Energy Storage System Based on MMC DC-DC Converter

In order to equip more high-energy pulse loads and improve power supply reliability, the vessel integrated power system (IPS) shows an increasing demand for high-voltage and large-capacity energy storage systems. Based on this background, this paper focuses on a super capacitor energy storage system based on a cascaded DC-DC converter composed of modular multilevel converter (MMC) and dual active bridges (DAB). The cascaded converter is called MMC-DAB for short. This paper analyzes the topology and modulation strategy of the system in detail. Taking into account the shortcomings of the traditional bidirectional power control strategy, this paper proposes a control strategy where the DAB module of each branch independently controls the voltage of the sub-module capacitor. The mathematical models of the traditional and the proposed control strategy are established. The stability of the two control strategies is analyzed and compared. Finally, a MW-level engineering prototype of the MMC-DAB energy storage system is designed and manufactured, and the effectiveness of the proposed control strategy was verified through experiments.