In power systems generation and control, the load variation has a great influence directly on the system's stability and dynamic performances. This paper describes the design of a compensator for a power system subject to random load voltage fluctuation, where the voltage fluctuations are treated as persistent functions satisfying bounding conditions. For stable operation and good performances of power systems, the rotor angle, the terminal voltage and the speed deviation of the generator are required to remain within their prescribed bounds, despite any change in the load voltage. Any violation of the bounds may lead to the system's instability and hence unacceptable consequences. The numerical results illustrate that the proposed design method provides a realistic formulation and therefore is effective for designing power system compensators.