TRANSMISSION ZEROS AND HIGH-AUTHORITY/LOW-AUTHORITY CONTROL OF FLEXIBLE SPACE STRUCTURES

Flexible space structures generally have very low levels of inherent damping, which makes the problem of controlling such systems quite challenging. For instance, unmodeled modes can easily be made unstable by spillover effects. One way to avoid these difficulties is to use a low-authority control loop to simply increase structural damping, typically to 5-10% of critical, and then use a more sophisticated high-authority control loop to achieve the desired control objectives. A very important design question that then arises is: what are the best choices of locations for the dampers used to implement the low-authority controller? This question is studied here, and it is shown that it is more important to increase the damping of the zeros of the damping-augmented structure than that of the poles. A simple algorithm is then derived for determining the damper locations that make the zeros as heavily damped as possible. Finally, the operation of this algorithm is illustrated by application to a simple cantilever beam example.