Model-free passivity-based control for grid-connected fuel cell systems

The increasing integration of distributed energy resources (DERs), particularly fuel cell (FC) systems, into low-voltage grids presents global challenges in ensuring grid stability and fault resilience. A critical issue is maintaining low-voltage ride-through (LVRT) capability of FC-based grid-connected voltage source inverters (VSIs) during grid disturbances such as voltage sags. Conventional control strategies fail to provide robust performance due to model dependency, poor dynamic response, sensitivity to grid parameter variation, and high computational complexity. This paper proposes a Model-Free Passivity-Based Control (MFPBC) technique that addresses these limitations. The method combines ultra-local modeling for real-time estimation of inverter dynamics with interconnection and damping assignment passivity-based control (IDA-PBC) to achieve robust and adaptive voltage and current regulation. Unlike traditional methods, MFPBC does not require prior system modeling and can support high X/R ratio networks under both symmetrical and unsymmetrical fault conditions. The proposed controller is implemented on a 50 kW FC-based VSI system and validated through both MATLAB simulations and OPAL-RT real-time hardware-in-the-loop (HIL) testing. Key performance metrics include transient suppression 1% , steady-state error minimization of 0.7%, reactive power support, and compliance with grid code-defined LVRT time constraints. Results show that MFPBC achieves superior dynamic response, enhanced robustness, and seamless fault ride-through capability.