Modelling of magnetizing inductance saturation in a three-phase self-excited induction generator

Abstract

Self-excited induction generators are used in small-scale generation systems such as small wind turbines and micro-hydro schemes where a grid connection is not available. In such applications, there is a strong need to model the generator as accurately as possible in order to obtain a realistic estimation of machine behaviour and dynamics. This study presents a generalized dynamic analytical model of a three-phase self-excited induction generator (SEIG) in the natural three-phase ABC/abc reference frame. The developed model accounts for the significant effects of magnetic saturation by expressing the magnetizing inductance as an exponential function of the magnetizing current, considering both variation in magnetizing inductance and its rate of change with magnetizing current (dLm/dim). This more accurately predicts the dynamic behaviour. The proposed model has the capability to include the effects of mutual saturation between the stator windings as well as that between the rotor windings. Additionally, the proposed model is extended to cover leakage saturation, such that, the effect of the derivative of leakage inductance with respect to magnetizing current is taken into account. The proposed dynamic saturated model is used to successfully predict the performance of the SEIG at steady state, load perturbation, faults, and balanced and unbalanced conditions. The results are verified experimentally using a 7.5kW induction generator test rig. A high level of agreement has been obtained between experimental waveforms and those from the proposed model.