Off-Equilibrium Linearization-Based Control of Nonlinear Time-Delay System and Application to a Turbofan Engine

Turbofan engines exhibit pronounced nonlinearity, so linearization has become a crucial link between turbofan engine control and linear control theory. Among linearization method, non-equilibrium linearization offers enhanced transient tracking accuracy and superior controller performance compared to methods operating near equilibrium points, making it more suitable for systems with rapid acceleration and deceleration, such as turbofan engines. Hardware-in-Loop (HIL) experiments are essential for verifying turbofan engine controller performance. However, time delay in the HIL platform can induce oscillations of state variables with controllers designed using this linearization method. To address this issue, this paper introduces an off-equilibrium linearization-based control strategy. This strategy employs a non-equilibrium linearized linear model to approximate the nonlinear time-delay system, followed by designing an H∞ controller for the linear time-delay system. The effectiveness of this approach applied to turbofan engines, including its anti-delay and robust tracking capabilities, is validated through simulations, HIL experiments, and semi-physical experiments.