Controls for transient operation of aircraft engine are highly important due to the fact that the transient performance depends on how the engine responds to throttle command via the control system. The Ndot control is widely used in modern aircraft engine that can produce a consistent acceleration/deceleration throughout the complicated engine conditions.
Two different forms of Ndot controllers are designed for a commercial turbofan engine, which are proposed in this paper. One controller is based on PI controller in tandem with an integrator. And the other is an integral controller associated with feedforward structure. The control structure also contains two cascaded 1-order filters in the feedback loop and a lead compensator on the forward path to improve transient response. The anti-windup design is highlighted in this paper, and a bumpless transfer can be expected during the entire MAX/MIN fuel selection process. The controller design procedure and parameter tuning are fully demonstrated to make the engineering approach more straightforward.
Those two control schemes are further evaluated and compared under engine nominal condition and deteriorated conditions via digital simulation. The simulation results are satisfactory and implicates that both of the controllers can meet the design requirements. The control accuracy of the one with feedforward structure is a little better than the other of PI with integrator. However, the latter design demonstrates better robustness and provides more consistent performance for all engine conditions.