Design of multivariable fixed-structural controller satisfying performance constraint on Nyquist diagram using frequency responses

In this paper, the stability condition and the robust performance condition are represented as a set of convex constraints with respect to the parameters of a linearly parameterized multivariable controller in the Nyquist diagram for the prespecified frequency points. This method can directly handle frequency-domain uncertainty without any modeling. Frequency-domain uncertainty can be minimized by appropriately selecting a nominal plant at each frequency point in the proposed approach. This paper proposes the design constraints to assure the desired control bandwidth and stability margin such as phase margin and gain margin to satisfy desired control specifications. The effectiveness of the proposed method is verified by comparison with the model-based approach by using μ-synthesis with the D-K iteration algorithm through an experimental result.