Model representations of induction motor group in power system stability analysis

With the aim to accurately take into account effect of dynamic loads in power system security simulations, investigation works get underway for representing a group of three-phase induction motors by an equivalent single-unit model or two-machine model. Inherent mechanical and extrinsic voltage characteristics of the induction motor are illustrated firstly. Based these characteristics, a method for calculating the parameters of the equivalent single-unit model is proposed. Then, properties extracted from the motor eigenvalues are used to classify a group of motors into two subgroups. The equivalent two-machine model is obtained from the two motor subgroups which can be used to modify some parameters of the single-unit model. Adequate treatments for equivalent inertia constant and rotor resistance ensure the single-unit model has high accuracy to simulate the original motor group under different large fault disturbances. Last, the proposed method is tested in a simple system, and the results show that the equivalent models and the original individual machines have nearly identical transient responses, even in some cases of system losing stabilities. The two-machine model is more accurate than the single-unit model.