Coordinated Flexible PV Operation and Fuel Cell Efficiency Tracking for Stable Microgrids with Grid-Forming Battery

Microgrids with grid-forming Battery Energy Storage Systems (BESS) face voltage and frequency stability challenges due to fluctuating loads and intermittent sources, such as photovoltaic power plants (PVPP). Especially when the BESS's state of charge (SOC) reaches its minimum limit <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(SOC_{min})$</tex>, causing under-frequency and battery depletion, leading to either load shedding or BESS damage. Conversely, over-frequency and overcharging occur when SOC reaches its maximum limit <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(SOC_{max})$</tex> due to excess PV generation, often mitigated by curtailing PV output through direct load following control, resulting in instability under rapid weather changes. This paper proposes two innovative strategies. First, to avoid load shedding at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$SOC_{min}$</tex>, we propose the integration of a fuel cell (FC) equipped with a flexible efficiency tracking controller based on a polynomial fitting technique, providing efficient power support without sacrificing fuel cell efficiency. Second, when SOC reaches <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$SOC_{max}$</tex>, we investigate coordinated flexible operation among multiple PVPPs with different irradiance conditions to manage excess generation without inducing stability issues. The proposed controller was rigorously tested across various scenarios.