Ripple Energy Buffer for Microgrid Connected Hydrogen Energy Storage System

An essential element of a distributed generation microgrid is an energy storage system that can accommodate the intermittency of the microgrid's renewable energy sources. Hydrogen energy storage systems (HESS), comprising an electrolyser and a fuel-cell, offer an attractive and green alternative for such a storage option, but care must be taken to avoid AC energy flow out of the fuel cell to prevent internal cell degradation. This is particularly important for single-phase microgrids, where the AC load current creates a double fundamental frequency harmonic current in the inverter DC bus. In this paper, the fuel-cell power flow is decoupled from this harmonic current flow by linking a capacitive energy buffer to the DC bus through a third phase leg on the inverter. This allows the inverter DC bus capacitance to be substantially reduced, thus improving the long-term reliability and robustness of the inverter and avoiding fuel-cell degradation. The concept has been proven by simulation and matching experimental results.