Power distribution strategy based on state of charge balance for hybrid energy storage systems in all-electric ships

During the navigation of all-electric ships, a hybrid energy storage system (HESS) is required to compensate power imbalance and maintain bus voltage stability. For a HESS composed of multiple energy storage (ES) devices, an unreasonable power distribution causes the ES devices with a low state of charge (SoC) to draw from power supply early, which deepens the operating pressure of the other ES devices. This in turn, affects the stable operation of the entire system. To achieve power distribution based on the SoC of different ES devices, a novel power distribution strategy for use in all-electric ships was proposed. In the proposed strategy, the virtual impedance of an ES device is connected with the SoC through exponential functions. As a result, the output power can be dynamically changed according to changes of the SoC. On the premise of obtaining a proper dynamic power distribution among ES devices with complementary characteristics, the SoC balance among ES devices with the same characteristics can be realized. Meanwhile, the bus voltage deviation induced by the virtual resistor is eliminated via an added compensation voltage. The effectiveness of proposed method is verified by both simulations and a StarSim hardware in loop (HIL) experimental platform.