Hierarchical Fuel-Cell Airpath Control: An Efficiency-Aware MIMO Control Approach Combined With a Novel Constraint-Enforcing Reference Governor

This article presents a hierarchical multivariable control and constraint management approach for an air supply system for a proton exchange membrane fuel-cell (PEMFC) system. The control objectives are to track desired compressor mass airflow and cathode inlet pressure, maintain a minimum oxygen excess ratio (OER), and run the system at maximum net efficiency. A multi-input multi-output (MIMO) internal model controller (IMC) is designed and simulated to track flow and pressure setpoints, which showed high performance despite strongly coupled plant dynamics. A new setpoint map is generated to compute the most efficient cathode inlet pressure from the stack current load. To enforce OER constraints, a novel reference governor (RG) with the ability to govern multiple references (the cascade RG) and the ability to speed up as well as slow down a reference signal [the cross section RG (CC-RG)] is developed and tested. Compared with a single-input single-output (SISO) airflow control approach, the proposed MIMO control approach shows up to 7.36% lower hydrogen fuel consumption. Compared to a traditional load governor, the novel cascaded CC-RG shows up to 3.68% less mean absolute percent error (MAPE) on net power tracking and greatly improved worst case OER on realistic drive-cycle simulations. Two fuel-cell system (FCS) models were used for development and validation, a nonlinear open-source model and a proprietary Ford high-fidelity model.