PULSE-WIDTH EQUIVALENT TO PULSE-AMPLITUDE DISCRETE CONTROL OF LINEAR-SYSTEMS

This paper presents a method to translate pulse-amplitude modulated discrete controls, for which many design algorithms exist, into pulse-width modulated controls extensively used in aerospace applications. Assuming that a discrete control law is available for a linear time-invariant multivariable system, the conditions for an approximate equivalent pulse-width application of the inputs are developed. The approximation is based on pulse, i.e., amplitude . duration, intensity equivalence, and on the evaluation of an optimum firing delay that maintains, independently from the control and external input, the dynamic performances of the system, including stability. A simple numerical example on a second-order system points out the benefits and drawbacks of the method, which is then applied to a typical complex aerospace design problem, i.e., shape and pointing control of a space antenna.