The role of active control in suppressing thermoacoustic instability

Continuous combustion processes commonly occur in systems of power generation, propulsion, and heating. A dynamic problem that is ubiquitous in these processes is thermoacoustic instability. What makes it particularly challenging to the control engineer is that this system is not only open-loop unstable, but has unstable zeros as well for certain actuator-sensor locations. The simultaneous presence of resonance and antiresonance characteristics places a considerable burden on the controller and poses constraints in its robustness properties. In a collaborative interdisciplinary effort at MIT, we have undertaken a systematic study of combustors and their instability properties. We have derived a model of the combustion process that captures the instability as well as the antiresonance properties and a model-based control design strategy for stabilization. An experimental combustor rig has been assembled to demonstrate and verify our analytical contributions. The paper presents the intricacies of the combustion instability and its active control, theoretical results from our feedback model and active control design, and experimental results using the model-based control. Our results demonstrate the power of active control, and the superiority and the ease-of-implementation of a model-based control design