Robustness characteristics of fast-sampling digital PI controllers for high-performance aircraft

The robustness characteristics of fast-sampling error-actuated digital set-point tracking PI (proportional plus integral) controllers are established in the case of partially irregular linear multivariable plants, i.e. plants with non-null rank-defective first Markov parameters and full-rank second Markov parameters. It is shown that the plant-parameter variations tolerable by such fast-sampling error-actuated digital controllers can be expressed very simply in terms of the step-response matrices of the nominal and actual plants. These general results are illustrated by examining the robustness characteristics of a fast-sampling error-actuated digital PI controller for three flight conditions of the F-16 aircraft