Dynamic inversion is a powerful tool for designing decoupling control laws for multivariable systems. An inherent feature of most dynamic inversion schemes is that the open-loop transmission zeroes become poles of the zero dynamics, which are theoretically unobservable in the controlled outputs. If these poles are unstable or very poorly damped they will adversely affect the closed loop. This issue is usually worked around by either approximating the offending non-minimum phase output by ignoring the derivative terms in a large zero or by redefining the output using a regulated variable, which approximates this output but is minimum phase. Both of these approaches produce inexact decoupling of the original outputs despite the fact that the regulated variables are decoupled. In this paper the approach is to exploit the fact that if the right-half plane zero is retained in the closed loop dynamics there will be no cancellation of that zero with an unstable pole. This approach requires an examination of the zero dynamics, which are governed by the transmission zeroes. This does constrain the form of the closed loop dynamics but does permit exact decoupling of the outputs, while maintaining stable zero dynamics. The idea is illustrated with an application to the lateral-directional control of the F18-HARV.
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