Phase balancing for a self-excited induction generator

Abstract

This paper describes a phase-balancing scheme for a three-phase self-excited induction generator (SEIG) which supplies single-phase loads. It is demonstrated that perfect phase balance can be achieved using a modified Steinmetz connection, provided that the positive-sequence impedance angle of the SEIG exceeds 2/spl pi//3 rad. From the phasor diagram, the conditions for perfect balance are established. It is found that the values of phase converter elements as well as the load resistance are functions of the positive-sequence admittance and impedance angle of the induction generator. Using the method of symmetrical components, the input impedance of the SEIG can be determined and solution of the equivalent circuit is formulated as a function minimization problem. The pattern search method of Hooke and Jeeves is employed for minimizing the impedance function, which enables the machine variables to be determined. It is further shown that, when the auxiliary load resistance is absent, perfect phase balance can still be achieved when the impedance angle of the SEIG is equal to 2/spl pi//3 rad. Feasibility of the phase-balancing schemes and the validity of the theoretical analysis are confirmed by experiments on a 2.2 kW induction machine.