Excitation balancing of a self-excited induction generator for maximum power output

Using symmetrical component techniques the steady-state behaviour of a self-excited three-phase induction generator under unbalanced loading is examined. Particular reference is made to single-phase loading, a practical application being the use of standard three-phase cage machines in micro-hydro plants. An unbalanced excitation scheme is proposed which improves balance overall and maximises the allowable power output of a particular machine. A method is presented by which de-rating factor and voltage regulation can be predicted for a general unbalanced condition. The results of modeling are in good agreement with experiment. Possible further applications of the method are to the behaviour of induction generators in networks and the operation of three-phase motors from single-phase supplies.