Comparative Study of Transfer Function Based Load Model and Composite Load Model

The composite load model consisting of an induction motor and a static load has been adopted by some utility companies in practical power system dynamic studies. Another form of dynamic load model is the transfer function based load model. Although both types of dynamic load models are well accepted, there is no comparison done regarding their performance, and no evaluation on the influence of voltage and frequency dependency terms on the overall model accuracy for transfer function based load models. In this paper, a transfer function based load model is developed analytically using a composite load model. Dynamic responses of the developed transfer function based load model and the original composite load model are compared subjected to various voltage and frequency disturbances. The transfer function based load model is a function of both voltage and frequency, three levels of simplifications are made to the full model in order to evaluate the corresponding accuracy. It is found the reduced model with both the 1storder voltage $\Delta \mathrm{V}$ term and 1storder frequency Δf term has the smallest error among the three reduced models.