A widely applicable, general methodology for estimation of traosfer function parameters from frequency response data is presented The procedure is bawd on tbe solution of a linear least squares pioblem by the singular value decomposition (SVD). The condition of the problem is discussed and approaclw refened to as shifting and scaling are introduced to reduce the condition number. To extend the application to practical caws with measurement emrs and/or a large number of poles, a partitioned estimation method with Gauss-Seidel iteratiws is develcped. M y , an iterative improvement process w i t h c " i n t s on the poles is applied to increase the accurscy and to avoid the possibility of obtaining unstable poles. The application of the suggested method of estimation to the ~presentation of transformers is pmented with practical examples. Elither transfer fuodion or state equation representation can be obtained for mawformers described by their terminal frequency responses.

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A direct method based on tlie linear least squares approach is applied for obtaining reduced order approximations of the propagation and characteristic admittance transfer functions of transmission lines for use in calculation of transients. The practical level of the acceptable error is discussed in terms of the precision of the frequency domain input data. The proposed approach provides satisfactory accuracy with a small number of ical and/or complex poles. The low order approximation could improve the efficiency of the E M " by reducing the computation time.