A Simplified Scheme for Scheduling Multivariable Controllers and its Application to a Turbofan Engine

Abstract

A simplified scheme for scheduling multivariable controllers for robust performance over a wide range of plant operating points is presented. The approach consists of scheduling only the output matrix of a dynamic controller, thus significantly reducing the number of parameters to be scheduled. Given a robust controller at a nominal design point, designed such that it gives a stable closed-loop system at various off-design operating points, the parameters of the controller output matrix are optimized such that the closed-loop response at the off-design points closely matches the design point closed-loop response. The optimization problem formulation for the synthesis of controller scheduling gains is discussed. Results are presented for controller scheduling for a turbofan engine for a conceptual Short Take-Off and Vertical Landing aircraft. The simplified controller scheduling is shown to provide satisfactory response for engine models corresponding to significant gross thrust variations from the nominal design point.