The H-infinity loopshaping design framework aims to synthesise a single unstructured compensator for a complete plant model. However, addressing problems such as air-vehicle control by partitioning the plant between modes (longitudinal, lateral and axial) and sequentially closing loops around objectives (body rate, incidence and climb angle) is intuitively more appealing and often practically desirable.
The presentation will go some way to modifying the H-infinity loopshaping framework so as to allow the design of such "partitioned" and "nested" feedback systems to be addressed. Specifically, a generalised form of Vinnicombe's nu-gap metric will be presented which allows the extra degree of freedom available in inner-loop model approximation to be exploited. While a simple inequality relating the obvious stability margins associated with a nested feedback system will point the way to methods of controller synthesis.
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