Model-based control of thermoacoustic instabilities in partially premixed lean combustion – a design case study

Abstract

Self-excited oscillation is becoming a major issue in low-emission, lean partially premixed combustion systems, and active control has been shown to be a feasible method to suppress such instabilities. A number of robust control methods are employed to obtain a feedback controller and it is observed that the robustness to system uncertainty is significantly better for a low complexity controller in spite of the norms being similar. Moreover, we demonstrate that closed-loop stability for such a complex system can be proved via use of the integral quadratic constraint method. Open- and closed-loop nonlinear simulations are provided.

Keywords:

• thermoacoustic instability
• equivalence ratio perturbations
• partially premixed flames
• model-based control
• controller complexity
• robust control

Acknowledgements

Postscript by the second author – it is a pleasure for me to contribute to this volume recognising the many contributions of Alistair MacFarlane to the field of control. Alistair was the Head of the Control Group and its corresponding Division in the Department of Engineering in Cambridge when I arrived in 1976 and until he moved on to Heriot-Watt in 1989. He was an exceptionally supportive and visionary head, leading a vibrant research community for which I remain most grateful.

The authors would also like to thank YC Chu, who was most helpful in the early stages of this research.