Robust eigenstructure assignment for multirate control systems

The design of feedback controllers for multirate digital systems is considered. The two main problems associated with such a scheme are the adverse effects of intersample cross-coupling and the large, switched control signals that normally result from a multirate feedback structure. The two problems present conflicting design objectives. Thus, a solution must seek to achieve an acceptable compromise between the minimization of control effort and the assignment of a prescribed modal structure. An optimized eigenstructure assignment method is developed to provide for this trade-off. The achievement of each design objective is governed by weighting factors in the optimization cost function. The design of a stability augmentation system for the lateral motion of an aircraft illustrates the application of this method