An n × n nonlinear plant that is known to be a member of a given set is given. The plant is embedded in a feedback structure in order to achieve desired closed-loop performances. The existing QFT technique for that purpose, based on replacing each nonlinear plant by an uncertain linear time invariant plant, is extended to design LTV controllers. In addition, a more efficient fixed-point theorem based on Homotopic invariance is used. The main results are that: (i) a controller with less control effort compared to a linear time invariant controller is achieved; and (ii) the class of plants and desired closed-loop specifications to which the technique can be applied is enlarged. A detailed design example is included.

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