L1L1 adaptive control for improving load-following capability of nonlinear boiler–turbine units in the presence of unknown uncertainties

• We analyze the uncertain operating conditions of nonlinear boiler–turbine control.
• We exploit a L1L1 adaptive controller for global, fast, robust and adaptive tracking.
• The closed-loop L1L1 stability and robustness under unknown uncertainties are proved.
• The offset-free input-to-state stable predictive controller functions as a reference.
• The L1L1 controller is evaluated to be better in performance and easier in design.

Uncertain operating conditions, along with the load demand for a wider and faster response, bring new challenges to the nonlinear boiler–turbine unit control. In order to achieve safe and efficient operations, this paper proposes a novel L1L1 adaptive state feedback controller for the multivariable nonlinear boiler–turbine systems with unknown uncertainties. This L1L1 adaptive control approach can achieve arbitrarily close tracking of the reference signal while ensuring closed-loop stability in the presence of strong nonlinearities, internal un-modeled dynamics, time-varying unknown parameters and uncertain dead time within its time-delay margins. In this study, a boiler–turbine unit simulation model is first built in order to verify the algorithm; then the L1L1 adaptive control approach is presented followed by its main results and proof; only based on one group of the equilibrium working point data, the L1L1 adaptive controller is designed for the overall working range of the boiler–turbine unit. For a more reliable evaluation on the L1L1 adaptive controller, the offset-free input-to-state stable fuzzy model predictive controller (OFISS-MPC) – which has all-sided performances – is briefly introduced and functions as a reference for our results. Finally, the L1L1 adaptive controller is tested in a series of challenging simulation scenarios and then compared with the OFISS-MPC controller. The results validate the expected performances of the L1L1 adaptive controller for the boiler–turbine unit with unknown uncertainties.