Abstract: This paper presents a new linear matrix inequality(LMI)approach to the mixedμ(structured singular value)analysis and synthesis problem. By using S-procedure, fl new μ upper bound for a dynamic system is derived in terms of LMIs. The proposed approach requires no high order multiplier and no frequency sweep. This approach is applied to a typical power system to solve the controller synthesis problem that guarantees the robust stability for a given variations in operating conditions. Numerical simulation results based on the presented control strategy are compared favorably with that based on classical AVR+PSS control.