Abstract
In this paper, we consider a quadratic stabilization problem based on H∞ controller. From the standard H∞ control theory, the transfer function of the closed-loop system is parametrized in terms of the linear fractional transformation on contract time-invariant parameters. We show that the closed-loop system is still quadratically stable when the time-invariant parameter is replaced by a time-varying gain. This comes from the lossless property that the two-port nominal system has. Furthermore, we show that the closed-loop performance can be improved by this time-varing gain. We give an example that illustrates the improvement of the zero-input response.
