The paper discusses, from a process control perspective, different approaches to performance weight selection when using H-infinity objectives. Approach A considers direct bounds on important transfer functions such as sensitivity and complementary sensitivity. Approach B considers the output response to sinusoidal disturbances, setpoints and noise. We also give some insight into the practical use of H-infinity and μ methods. μ is the structured singular value (SSV) introduced by Doyle (1982). μ-synthesis is generally not a convex optimisation problem and is presently not straightforward. We will discuss some of the problems we have encountered.
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