STABILITY MARGINS AND MODEL-REDUCTION

A new method is proposed which can be applied to the ''primary reduced model'' determined by any convenient method, to obtain an ''enhanced reduced model'' so that the frequency response of the original high-or der model can be matched by the enhanced reduced model at the desired critical frequency points, such as gain-crossover, phase-crossover, et c. of the overall system. As expected, and shown in the examples, the stability and performance characteristics of the system with the enhan ced reduced model will more closely approximate that of the original s ystem compared to the system using only the primary reduced model of t he same order. The proposed method can be applied equally well to open -loop model reduction and sampled-data control systems analysis. Examp les are given to illustrate the method and its applications.