Fuzzy Fuel Flow Selection Logic for a Real Time Embedded Full Authority Digital Engine Control

Abstract

The control logic of the modern Full Authority Digital Engine Control (FADEC) is comprised of many control loops, each of which has a specific purpose. Typical control loops include (but are not limited to) a high or low rotor speed governor, an Acceleration and Deceleration loop, and various limiting loops for temperature, speed, fuel flow, and rate of change of fuel flow. The logic that determines which of these loops is “in control” at any particular time has a history of being very simplistic. This Selection Logic is usually nothing more that a cascade of minimum and maximum selection logic gates. Since this logic is so simplistic, the control engineer often has to “fine tune” the compensator design for each loop, in order to achieve proper performance. The purpose of this paper is to a present a means of achieving a selection logic design based on Fuzzy Logic principles. Hereafter, this shall be referred to as a Fuzzy Fuel Flow Selector. The paper provides a brief overview of the most typical architecture for real time embedded FADEC control logic, rule development for the Fuzzy Fuel Flow Selector, and a realistic implementation of the Fuzzy Fuel Flow Selector. Also provided is a typical application that is used to contrast the performance between traditional selection logic and the Fuzzy Fuel Flow Selector. An overview of the Fuzzy Logic process is also included for completeness.