NEURAL NETWORK BASED ACTIVE CONTROL OF UNSTABLE CO... Copyright © 1999 IFAC 14th Triennial World P.R. China 14th World Congress of IFAC J-3e-02-5 NEURAL BASED AC'"fIVE C()NTROL OF UNS'"fABLE COMBUSTION SYSTRl\-IS GP Liu and S Daley ALSTOM Energy TechnologJ' Centre. Catnbri{lge ROUtl, Leicester LE8 6LH, lJK Fax: +44 116 201 5464. L'lnail: guoping.liu@energ.-r.alstoln.coln dale)' @ e 12 e rgy. a !SIOnL co In Abstract: This paper is concerned "vith active stabiJisation of unstahle cnnlbustion systenlS using neural net'\-\'orks. A novel active control strategy is. proposed. Jt is comprised of three parts: an output modeL an output predictor and a feedback controller. The output model is established using neural net\vorks to model the measured output. To overcome the thue delay of the syst.enl, which is ofLen very large compared the saolpling the output predictor is developed using the output model.U"nHke a classical observer (e.g., state observer), only a measured output signal is required. An output-feedback controller is introduced which uses the output of the predict.or. The approach developed is firsl demonstrated using a simulated unstable combustor with six modes. Results are also presented sho\ving its application to an experimental combustion facility using a loudspeaker actuation device. @ 1999 IFAC Keywords: Neural networks, combustion unstable prediction. 1. INTRODUCTION Comhustion processes exist in luany applications related to po\ver generation, heating and for example, steam and gas turbines, domestic and industrial burners 1 and jet and r31ujet engines. The characteristics of these processes includes not only several in teracting physical phenomena but also a \vidc variety of dynarnic behaviour. In terms of their impact on the system pressure oscillations are the most significant. In some applications, the pressure oscillations are undesirable since they result in excessive vibrations causing high level of acoustic noi:;;c and perhaps mechanical failures. the pressure oscillatjons change with the operating condition of the combustor so it is diflicult to Jneet specific pcrfomlancc criteria. Copyright 1999 IFAC Generally there are two types of control strategies for the combustion characteristics: passive control and active control. Passive control has heen used in most practical combustors. The passive control approaches include changing the flame anchoring the burning and acoustic boundary conditions, and installing bafOes and acoustic dampers (Schadow and 1989). ACLive control has also been used as a means for reducing pressure oscillations and pollutant fonnation. Many active control approaches have been applied to combustion for example phase-lead control (l\1aManus et al'-r robust control (Tierno and Doyle, 1992), LQG control (Annaswamy and Ghoniem, 1995), adaptive control (Padnlanabhan et a1. 1995). In order to develop an effective active controller for unstable ISBN: 0 08 043248 4 5123