On the Design of Two-Degree-of-Freedom Multivariable Feedback Control Systems

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This research proposes a methodology for designing two-degree-of-freedom (performance and stability margin) multivariable feedback control systems. A quadratic cost functional is used to measure such performance attributes as tracking error, saturation, and sensitivity to small plant perturbations. Stability margin is measured with an L-infinity norm on an appropriately chosen stability margin matrix. A mechanism for tradeoff between performance and stability margin will be investigated. This mechanism is different from the one recently described in the literature and shows promise of being more powerful. In addition, the choice of the stability margin matrix will be investigated. Another important consideration in the design of multivariable control systems is decoupling (each command input controlling only one output). The structure proposed here is well suited to the decoupling problem since it permits the separation of the problem of decoupling from the problem of realizing a desirable stability margin. There is, however, a decoupling constraint which can deteriorate achievable performance. A portion of this research will be directed towards developing a design procedure which minimizes this performance deterioration.