L1 adaptive output feedback controller with operating constraints for solid oxide fuel cells

Control on solid oxide fuel cells (SOFC) is challenging due to its nonlinearity, time-varying uncertainties, tight operating constraints and modeling difficulties. The L1 adaptive output feedback controller for systems of unknown relative degree is introduced for the SOFC output voltage control in this paper. It allows for fast and robust adaptation, and provides improved transient performance. Its advantages of not enforcing a strictly positive real condition along with the low-pass filtered control signal bring it the potential to be applied in wide industrial processes. In the study of the SOFC control, a dynamic SOFC model is first built; then a L1 adaptive output feedback controller is designed only using the nominal working conditions of the SOFC model. Through setting the operating constraints at proper locations, the closed-loop stability is maintained in the presence of hard constraints by the symmetric structure of the L1 adaptive control loop. A simulation comparison is made in the SOFC constant voltage control process between the L1 adaptive controller and a linear disturbance model predictive controller (DMPC) for their almost equal complexity in designs. The result shows the advantage of the L1 adaptive controller in disturbance rejections for its faster transient response.