Improved internal-model robust adaptive control with its application to coordinated control of USC boiler-turbine power units in flexible operations

Coordinated controllers for coal-fired ultra-supercritical (USC) boiler-turbine power units in the new flexible-operation mode face many challenges, such as faster load-following rate over wider-range operations, nonlinear dynamics with long time delay and multiple disturbances from strong-coupled multivariable processes. Hence, to improve the coordinated controller of the USB power unit, this paper proposes an internal-model robust adaptive control (IM-RAC) approach to handle nonlinearity, multiple variables, unknown uncertainties and long-time delay. The proposed IM-RAC augments an internal model with the framework of an L1 robust adaptive control to predict the time-delay variable. In addition, the proposed IM-RAC uses a dual-feedback adaptive law instead of a single-feedback adaptive law. Based on the proof by contradiction, the stability of the IM-RAC control loop is proved, and stability conditions and performance bounds are derived. Furthermore, an IM-RAC coordinated controller is designed for a 1000 MW coal-fired USC power unit. By simulations, we show that the proposed IM-RAC outperforms an advanced model predictive controller in the presences of fast and wide load-following, long-time delay and uncertainties. With less modelling requirements, the IM-RAC control approach is a promising solution to improve the operational flexibility of USC power units.