Integrated Turboshaft FADEC Architecture and the Effect of Governor Implementation on Protection-Layer Loading

Abstract

Comparative studies of turboshaft fuel controllers commonly report performance advantages without holding the loop bandwidth or anti-windup implementation constant across the compared configurations. This paper asks what survives such a comparison. An integrated FADEC architecture for a GE T700-class turboshaft is developed on a nonlinear T-MATS model, combining a power turbine speed governor, a two-dimensional variable guide vane schedule, actuator and sensor dynamics with transport delays, and a seven-channel min–max protection layer. Three governors (gain-scheduled PI, fixed-gain PI and integral sliding-mode) are evaluated with identical anti-windup implementations, with their loop bandwidths matched by construction at the hover operating point used for the load-disturbance tests. Transient performance is closely comparable, with overshoot during scheduled transitions differing by at most 0.25 percentage points; however, protection-layer loading is not, as the sliding-mode governor holds the limiters active for 9.2% longer than the baseline under load disturbance. Removing the anti-windup tracking path changes cumulative limiter engagement by 6.6 times the difference attributable to the control law; the ordering survives both sensor noise and a ±20% perturbation of the power turbine inertia. Within the tested architecture, the dominant coupling between speed governance and engine protection is associated with the anti-windup implementation rather than the control law. Automatic code generation yields 37% less algorithm code for the sliding-mode configuration, with software-in-the-loop verification at a fixed 5 ms step.