HYDROGEN AND BATTERY – BASED HYBRID ENERGY STORAGE SYSTEM (ESS) FOR FUTURE DC MICROGRIDS
Energy Storage systems (ESS) are used to store excess Renewable Energy Resources (RES) to help meet the power grid requirements. Different energy storage devices have different strengths and weaknesses. Battery, for example, has a high-power density capable of providing power almost instantaneously, while hydrogen has a high energy density capable of providing power for a long period of time. In order to take advantage of their unique aspects, there can be used in conjunction with each other in what is called a Hybrid Energy Storage System (HESS). In the first part of this work, a hydrogen-based ESS for DC microgrid, which can potentially be integrated with battery ESS to meet the needs of future grids with high renewable penetration, is investigated. A challenging aspect of this system is the integration of power electronics with fuel cell technology to convert RES into electricity seamlessly. A phase Shifted Full Bridge (PSFB) converter is used as a step-down transformer to activate clean hydrogen production during the electrolysis. The stored hydrogen is transformed into electricity when needed to balance demand and supply. The proposed system simulates aspects of the power conversion, electrolyzer, storage tank, and fuel cell needed for the proposed hybrid ESS. The second part of this work explores the implementation of the proposed system's optimal energy management (EMS) to minimize its operation and battery degradation cost. The optimized system will not only schedule the distributed energy resource (DER) and exchange power with the main grid, but it will also consider selling back power to the grid to minimize the cost of the system. The objective function formulation minimizes the operation cost of the system and also limits the battery charging rate to prioritize hydrogen storage during high penetration of the RES and avoid rapid degradation of the battery. As in the first part of this work, the second part will also optimize the different aspects of the hybrid ESS to maintain a reliable system operation by carefully managing supply and demand between the two storage and limiting constant use of the battery, thus increasing its lifetime.