Sliding mode control for longitudinal oscillating combustion

Considerable research has been reported on developing effective active control means to suppress oscillating combustion. The typical pressure oscillation can be divided into linear growth, transition and saturation stages. In this study, a sliding mode control strategy, consisting of a state estimate model, disturbance observers and a sliding mode controller, is proposed to suppress the longitudinal oscillating combustion. The control strategy is first tested with a nonlinear 0D state space model as the controlled plant. Results show that the state estimate model combined with the singular spectrum analysis (SSA) method can accurately estimate the system state quantities by grouping the SSA modes according to the frequency difference and calculating mode envelopes. To ensure the estimate accuracy, the number of truncated SSA modes varies according to the oscillation stage. The disturbance observers are designed to improve the robustness of the controller by introducing broadband spectrum disturbance to account for the external noise in the observed values. The sliding mode controller can limit the disturbance amplitude, and effectively suppress the pressure oscillation. A 1D Rijke tube acoustic network is also tested to further validate the controller adaptability. With this controller, the Rijke tube pressure oscillation can be effectively eliminated when control starts at the linear growth, transition, or saturation stages.