Control design with output constraints: Multi-regulator sliding mode approach with override logic
The problem of setpoint regulation of a main output with constraints in a set of secondary outputs is considered. Specifically, a main output is to be regulated to a setpoint using a single control input, while preventing secondary outputs to cross prescribed limits. When the outputs are minimum-phase, previous work by the author shows that a set of sliding mode regulators arranged in a max-min override scheme with input integration achieves the output regulation and limit protection objectives, with guaranteed stability, maximal exploitation of available limits, and straightforward design guidelines. In this paper, no input integration is used, removing a limitation of the previous approach that required secondary outputs to have a nonzero feed-through term. Design of the sliding coefficients for the main regulator is also considered using mixed H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> feedback synthesis. A detailed numerical example is included.