Discretization of power system transfer functions

This paper compares two methods for obtaining a discrete-time mathematical model for digital control design of a power system. The usual approach has been to use the shift operator q, or its equivalent z-transform, but this gives numerical difficulties with the small sampling periods which are now becoming usual with modern control hardware. It is shown, by means of the example of the identification of a generator excitation control system, that these problems can be avoided by the use of the delta operator δ instead. Calculations show that the δ-operator formulation also reflects the frequency and dynamic response of the system more accurately and conveniently