A new technique was presented that facilitates design of independent full-state feedback controllers at the subsystem levels. Different types of local controllers, for example, eigenvalue assignment, robust, optimal (in some sense ) may be used to control different subsystems. This feature has not been available for any other known linear feedback controller design technique. In the second part of the paper, we specialize the results obtained to the three time-scale linear control systems (singularly perturbed control systems) that have natural decomposition into slow, fast, and very fast subsystems. The proposed technique eliminates numerical ill-conditioning of the original three-time scale problems. The newly proposed three-stage feedback controller design is demonstrated on the eighth-order proton exchange membrane fuel cell model.