Active Control of Thermoacoustic Instability Using a Model-based Approach

Recently, active control has been pursued vigorously for combating thermoacoustic instabilities in the combustion process. While many of the reported experiments, with controllers that include filter components determined by trial and error, have demonstrated that the dominant thermoacoustic instability can be suppressed, often the response contains secondary peaks at other frequencies which were not excited in the uncontrolled combustor. In this paper, a physical systematic model-based design of an active controller for suppressing thermoacoustic instability which overcomes many of the drawbacks of the experimental controllers is presented. This model takes into account laminar flame kinematics and linear acoustic dynamics with coupling between the acoustic modes and actuation using an end-mounted loudspeaker. With this model, a model-based controller which results in a distinctly improved performance over the experimental controllers is designed. This controller is based on an optimization strategy and leads to significantly faster settling time of the pressure oscillations, exhibits no secondary peaks, and uses smaller control effort.