Digital controller design for the pitch axis of the F-14 using an H^∞ method

An H^∞-based control system design procedure is developed to produce a controller in which the closed-loop system is designed, using H^∞ methods similar to those of H. Kwakernaak (see Int. J. Control, vol. 44, no. 1, pp. 117-156, 1986), to be robust with respect to both disturbance rejection and insensitivity to parameter variations. The H^∞ design approach is coupled with multicriterion optimization to design a pitch-axis controller for the F-14 aircraft. The design problem is an augmented version of one of two CSS benchmark problems. The authors design a discrete-time controller even though the benchmark is in continuous time. The benchmark, while specifying gain and phase margins, does not specify the expected ranges for the parameters of the plant. Estimates have been obtained of the reasonable ranges of parameter variations, which are checked against the design. The precompensator is used to shape the output response so as to cause the entire system to achieve the desired performance. The robustness of the angle-of-attack response under large parameter variations is examined. A satisfactory design has not yet been obtained. However, these intermediate results are thought to be of value in demonstrating the difficulty of the problem and the thought processes involved in trying to use H^∞ methods to solve a realistic design problem.