With the relevant theories fully developed, sliding mode control (SMC), a kind of nonlinear control strategy having particularly strong robustness and disturbance rejection properties, has been applied in a considerable number of fields, such as robotic manipulator control, power generation control in wind turbines, robust stepper motor control, etc. For aero engines, remarkable progress of adopting SMC has been made. For instance, Richter has published his research of limit management in aircraft engine controls which suggests that replacing the linear regulators with sliding controllers can overcome the obstacle of traditional min-max approach.
It is revealed from publication that researchers who design sliding controller for aero engines have made every effort to focus on the sliding surface and control law of SMC while they seldom paid attention to the constraints in actuators, such as saturation and rate limitation. In practical engineering, the performance of the ideal controller is infeasible under the situation that unavoidable constraints exist. Although the actuator saturation can be avoided by introducing a velocity form controller, rate limitation can still degenerate the control performance severely.
In this paper, therefore, the design of a sliding controller for aero engines with rate limitation is discussed. A speed tracking problem is described based on the engine model simplified from a nonlinear system to a piecewise linear system at selected equilibrium points. A sliding surface is defined as the generalized tracking error, and a SMC law is designed with Lyapunov analysis of the closed loop system. Simulation results verify the stability of the closed-loop system, and show that the proposed sliding controller is capable of regulating a turbofan engine for large thrust commands in a stable fashion with proper tracking performance, which can mitigate the negative effect of actuator rate limitation.