A novel representation of a.c. machine models in terms of multiport networks have been presented. These networks are based on the lumped-parameter models and are derived for the two basic a.c. machine structures, i.e. the smooth air-gap structure, and the salient-pole structure. The models feature the same number of terminals as the real machines that complies with requirements for modelling and simulation of power electronic converter-electrical machine systems. In particular, these models eliminate a general difficulty encountered in the automatic formulation of the conventional two-axis a.c. machine model terminal-constraints, imposed by the operations of converter-machine units at normal and/or fault modes. Other important feature is the direct implementation of the stable numerical integration algorithm, based on the associated discrete circuit models of reactive network elements. To enhance the models accuracy, electromagnetic non-linearity effects are introduced properly through developed saturation factors which consider the mutual-axis saturation dependance. Finally, it should be noted that the presented models are amenable to incorporation in computer-aided power electronic systems design packages and in general-purpose simulators, such as PSpice and SABER. The properties of the presented models have been verified for different converter-machine systems on the field. As an illustrative example, simulation and measurement results for the laboratory induction motor drive system with a squariwave VSI in the stator and for the industrial induction motor drive system with converter cascade in the rotor have been presented.
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