Unknown system dynamics estimator based coordinated control of the ultra supercritical boiler‐turbine unit with coal pulverizing delay for large load accommodation

Abstract

AbstractThe ultra‐supercritical boiler‐turbine unit is required to accommodate large‐range load following to maintain the stability of grid frequency. However, the input delay in the coal pulverizing process poses a challenge to the coordinated control of the boiler‐turbine unit, which is always neglected in existing works but dramatically affects the stability of steam pressure and temperature. In this paper, to handle the delay caused by coal pulverizing, a predictor‐based delay compensation structure is developed for producing a delay‐free control framework for the throttle steam pressure. Moreover, to overcome intrinsic nonlinearities in the dynamics of the boiler‐turbine unit, the unknown system dynamics estimator is employed in the controllers' design for the steam enthalpy in the separator and active power of the turbine. Thus, precise and fast regulation for the active power output can be achieved under wide load following task. The salient merit of the proposed control is that the overshot of the throttle steam pressure and the specific enthalpy in the separator can be significantly alleviated, which is necessary for turbine blade. A Lyapunov‐Krasovskii functional is introduced to deal with the time delay in the stability proof. Finally, the proposed coordinated control is validated in three typical working scenarios.