Completely Decentralized Energy Management System for Fuel Cell-Battery-Ultracapacitor Hybrid Energy Storage System

For the fuel cell-battery-ultracapacitor hybrid energy storage system applied to the transportation electrification system, its energy management system (EMS) has to achieve the expected energy management objectives, including dynamic load power-sharing, state-of-charge regulation of battery and ultracapacitor, and regenerative braking capability, etc. Conventionally, such an EMS is achieved in a centralized or hierarchical way, resulting in poor flexibility, scalability, and reliability. In this paper, a completely decentralized EMS, which is achieved based on a modified mixed droop control, is proposed to achieve the above objectives. As the implementation of the proposed EMS does not rely on any communication links or common signals, the system cost is reduced. Besides, the system with the proposed EMS is of high reliability as it can still operate well during the outage of one power source due to malfunction. The operational principle of the decentralized EMS is analyzed in detail, followed by which the system design is elaborated. In the end, the feasibility and effectiveness of the proposed EMS are verified by experimental results.