Fuzzy wide-range control of fossil power plants for life extension and robust performance

This paper presents a fuzzy-logic-based methodology of life extending control (LEC) for robust wide-range operation of fossil power plants including load-following, scheduled shutdown, and hot startup. The objectives of the LEC are performance enhancement and structural durability of both aging and new fossil power plants. The proposed control system has a two-tier architecture, which explores and optimizes the plant performance and structural durability trade-off. The lower tier consists of a feedforward control policy and a family of linear multivariable robust feedback controllers, which are gain-scheduled for wide-range operation. The sampled-data feedback control laws are synthesized based on an induced L₂-norm technique that minimizes the worst-case gain between the energy of the exogenous inputs and the energy of the regulated outputs. The supervisory controller at the upper tier makes decisions on plant operations with due consideration to structural durability of critical plant components (e.g., steam generators, steam headers, and turbines). The supervisory controller is synthesized based on approximate reasoning embedded with rule-based expert knowledge of the power plant and analytical models of structural damage. Using the fuzzy logic, the plant operation strategy is modified on-line for trade-off between plant performance and structural damage in critical components. The fuzzy algorithm facilitates bumpless controller switching for gain scheduling under wide-range operation and control. It also adds robustness to the control system especially if the lower tier of gain-scheduled controllers is not able to maintain stability under plant perturbations.