Stable Partial Pade Approximations for Reduced Order Transfer Functions

While the Pade approximation can often be used to produce good reduced order transfer functions, the method suffers from the disadvantage that a stable reduced order model is not always obtained for an original model that is stable. A method is described for obtaining stable partial Padé approximation reduced order models. The method permits the determination of the effect of changes in the coefficients in the partial Padé approximation on the poles of the reduced order transfer function by means of standard root locus plots.