Advanced boiler/turbine control and its benchmarking in a coal-fired power plant

The performance of robust multi-input-multi-output (MIMO) controllers designed for the megawatt output/throttle pressure control in a boiler/turbine unit of a coal-fired power plant using the H _∞ optimization is evaluated. First, a comparison of the performance of a standard H _∞ controller with that of the linear multi-loop PID-based controller exhibiting performance very close to that of the currently employed nonlinear PID-based controller is carried out using the linear plant model. This comparison shows that the H _∞ controller provides significantly lower performance deterioration under typical variations in plant dynamics. However, when the H _∞ controller is implemented on the plant simulator that incorporates the actuator (steam valve) nonlinearity, its performance is found to be characterized by the excessive quasi-steady-state oscillations of the plant output. To address this problem, a modification of the robust control law referred to as the setpoint conditioning is developed. Simulations demonstrate that the resulting conditioned H _∞ controller displays performance and robustness significantly superior to that of the currently employed nonlinear PID-based controller. In order to benchmark the robust controllers against the PID-based ones on the actual plant, a novel state/output bumpless transfer technique is presented that permits smooth switching between the online and the offline controllers under the limited knowledge of the actual dynamics of the controllers implemented in software/hardware.