1994 Volume 114 Issue 11 Pages 1099-1108
This paper deals with descriptive methods of differential equations as models of actual power system loads. Two classes of descriptive methods are discussed: description using power and voltage as descriptive variables (input/output description); description using state variables as descriptive variables (state variable description). Input/output description is frequently used for description of the general types of load actually measured at the load buses of power systems, while state variable description is ordinarily employed for descriptions of individual load devices. The following topics are specifically described. (1) Two descriptive methods are compared principally from the viewpoint of practicality, and state variable description is shown to be advantageous for many types of analysis. (2) The concept of transformation from input/output description to state variable description is described using block diagrams. (3)The transformation is applied to a first order nonlinear load model. (4) The instantaneous load characteristic is introduced as the concept related to the transformation.