Mixed H2/H[infinity] Robust Controller Design with Degree Constraint in Angular Metric

In the framework of the angular metric, robust stability margin is used to characterize the stability robustness of the closed-loop system. The mixed H
₂
/H
_∞
robust controller with degree constraint is designed, whose degree is not larger than that of the plant. The characteristics of mixed H
₂
/H
_∞
controller with degree constraint are discussed, and the form of the controller is parameterized. After that, we get the constraint conditions and the interpolation equations. The mixed H
₂
/H
_∞
controller can be synthesized by solving the nonlinear equations, where a modified Newton method is proposed. In comparison with the LMI controller and the central controller, the mixed H
₂
/H
_∞
robust controller has the best LQG performance when the robust stability margin is given.