H∞ mixed-sensitivity optimization method has been utilized to design controllers that robust to variation of system operating conditions and transmission delays. The H∞ technique, however, is restricted to dealing with multiplicative or additive uncertainty and can lead to conservative controller performances in the case when there is more than one structured uncertainty. Compared to H∞ approach, the structured singular value (SSV or μ) technique is more appropriate for controller design where multiple parametric uncertainties have to be considered. This paper presents the work of uncertainty modeling and proposes a μ synthesis framework to design a controller robust to both system uncertainty with respect to varying operating conditions and delay uncertainty associated with the wide-area signal transmission. The numerical results have shown that the proposed μ controller can stabilize the system and enhance the damping performance over the specified range of uncertainties compared to the conventional H∞ controller.