Disturbance rejection of nonlinear boiler–turbine unit using high-order sliding mode observer

It is interesting and challenging to develop advanced controller for industrial boiler-turbine units due to their genuine nonlinearities, serious couplings among state variables, physical constraints imposed on control inputs, and in particular, various types of unknown uncertainties/disturbances. In this paper, a nonlinear disturbance rejection control method is investigated in a composite design manner for an oil-fired drum-type boiler-turbine unit. A baseline exponentially stable feedback controller is first designed, and then a high-order sliding mode observer is utilized to estimate and thus to compensate unknown lumped disturbances. It is shown that the obtained results for the boiler-turbine unit can be extended to a wide class of nonlinear systems. More interestingly, the finite-time stability of the closed-loop systems can be rendered in several cases. Finally, some numerical simulation scenarios are conducted on the boiler-turbine unit to demonstrate the claimed control performance.