Model-based control of combustion instabilities in annular combustors

Lean premixed combustors produce lower NO_x emissions, but are particularly prone to damaging combustion instabilities. Active control can be used to stabilize combustion instabilities. So far model-based control strategies have tended to focus on longitudinal rather than annular combustors, even though many gas turbines have annular geometries. In this work, a computational thermoacoustic model is used to simulate unstable annular combustors, providing a platform on which to develop and test control strategies. The model contains multiple fuel valves for actuation, which respond to multiple pressure sensors according to a controller matrix. Two strategies for designing the controller matrix are developed. The first involves stabilizing each of the unstable circumferential modes independently; the second involves controlling the transfer function matrix between sets of actuators and sensors. The resulting controllers are implemented in simulations using the thermoacoustic model. They are seen to stabilize instabilities in a variety of combustors, including one with nonaxisymmetry due to burner differences and one with both circumferential and longitudinal unstable modes.