Abstract: A new design method of robust controller is discussed in this paper. This method finds a state or output feedback with fixed gains such that the stability and dynamic property of a system are robust with respect to large plant parameter variations and so on. The required magnitude of control inputs is kept small in this design. The system property considered in this paper is "nice stability and dynamic property" as specified by a region in the eigenvalue plane, in which all eigenvalues have to remain in spite of perturbations. In this paper, the design method based on the eigenvalue plane is discussed from simple to complication and the complicated mathematic calculation is avoided. Using graphic method or computer aid design, the controller becomes a robust controller with the nice stability and dynamic property. A specific design of a certain type of flight control system is also introduced and satisfactory simulation results are obtained.

Key words: robust control, feedback, eigenvalue, fixed gain