Reducing the effects of model reduction on stability boundaries and limit-cycle characteristics

In this note, the effects of model reduction on the stability boundaries of control systems with parameter variations, and the limit-cycle characteristics of nonlinear control systems are investigated. In order to reduce these effects, a method is used which can approximate the original transfer function at
s = 0
,
s = \infty
, and also match some selected points on the frequency response curve of the original transfer function. Examples are given, and comparisons to the methods given in the current literature are made