Difference Between Fixed-Structure Tuning and Traditional H-Infinity Synthesis
All of the tuning commands
hinfstruct tune the controller parameters by
optimizing the H∞ norm
across a closed-loop system (see ). However, these functions differ in important
ways from traditional H∞ methods.
Traditional H∞ synthesis
(performed using the
designs a full-order, centralized controller. Traditional H∞ synthesis
provides no way to impose structure on the controller and often results
in a controller that has high-order dynamics. Thus, the results can
be difficult to map to your specific real-world control architecture.
Additionally, traditional H∞ synthesis
requires you to express all design requirements in terms of a single
weighted MIMO transfer function.
In contrast, structured H∞ synthesis allows you to describe and tune the specific control system with which you are working. You can specify your control architecture, including the number and configuration of feedback loops. You can also specify the complexity, structure, and parameterization of each tunable component in your control system, such as PID controllers, gains, and fixed-order transfer functions. Additionally, you can easily combine requirements on separate closed-loop transfer functions.
 P. Apkarian and D. Noll, "Nonsmooth H-infinity Synthesis," IEEE Transactions on Automatic Control, Vol. 51, Number 1, 2006, pp. 71-86.