A thrust estimation and control method of an adaptive cycle engine based on improved MFAC algorithm

The development of the adaptive cycle engine is a crucial direction of advanced fighter power sources in the near future. However, this new technology brings more uncertainty to the design of the control system. To address the versatile thrust demand under complex dynamic characteristics of the adaptive cycle engine, this paper proposes a direct thrust estimation and control method based on the Model-Free Adaptive Control (MFAC) algorithm. First, an improved Sliding Mode Control-MFAC (SMC-MFAC) algorithm has been developed by introducing a sliding mode variable structure into the standard Full Format Dynamic Linearization-MFAC (FFDL-MFAC) and designing self-adaptive weight coefficients. Then a trivariate double-loop direct thrust control structure with a controller-based thrust estimator and an outer command compensation loop has been established. Through thrust feedback and command correction, accurate control under multi-mode and operation conditions is achieved. The main contribution of this paper is the improved algorithm that combines the tracking capability of the MFAC and the robustness of the SMC, thus enhancing the dynamic performance. Considering the requirements of the online thrust feedback, the designed MFAC-based thrust estimator significantly speeds up the calculation. Additionally, the proposed command correction module can achieve the adaptive thrust control without affecting the operation of the inner loop. Simulations and Hardware-in-Loop (HIL) experiments have been performed on an adaptive cycle engine component-level model to investigate the estimation and control effect under different modes and health conditions. The results demonstrate that both the thrust estimation precision and operation speed are significantly improved compared with Extended Kalman Filter (EKF). Furthermore, the system can accelerate the response of the controlled plant, reduce the overshoot, and realize the thrust recovery within the safety range when the engine encounters the degradation.