Analysis and use of several generalized ℋ(∞ mixed sensitivity frameworks for stable multivariable plants subject to simultaneous output and input loop breaking specifications

In this paper, we present and examine three generalized mixed-sensitivity control design frameworks for linear time invariant (LTI) plants for trading off properties at distinct multivariable loop-breaking points, while being able to handle a broad class of closed loop (e.g. ℋ^∞, ℋ², frequency- and time domain) specifications. Multiobjective tradeoff paradigms are developed and analysed for ill-conditioned plants having large relative gain array entries - plants that have received considerable attention in the literature without yielding a direct systematic design methodology. We provide insight into the effectiveness of each approach and discuss the trading-off of properties at distinct loop-breaking points. This is done by exploiting the Youla-Jabr-Bongiorno-Kucera-Zames (YJBKZ) parameterization, the resulting convexification, and efficient state-of-the-art convex solvers that can be applied to smooth as well as non-differentiable problems. Moreover, we also show how our approach can be applied to multivariable infinite-dimensional plants. Specifically, by using finite dimensional approximants that converge in the uniform topology, we obtain near-optimal finite dimensional controllers for the infinite dimensional plant. Illustrative examples are provided for a thermal PDE and a retarded time delay system.