Self-stimulation Of The Three-phase Induction Generator Steady-state Operating Performance

The equivalent circuit of self-excited induction generators is mathematically modeled by referring the stator and rotor voltage equations to the base frequency respectively. For the convenience of computation, an iterative method is proposed to predict the steady-state performances, in which the technique for simplifying equations is utilized. By lowering the equation order, a new formula containing only one unknown variable is set forth, the order of which is as low as 2. The iterative process, which avoids lengthy and tedious algebraic derivation, has shown its rapid convergence and flexibility for further analysis. Calculated results are compared with the experiment values, which show a good agreement between them.In view of the poor inherent external voltage characteristics of self-excited induction generators, long-shunt compensation capacitors, short-shunt compensation capacitors and shunt compensation capacitors are utilized for voltage stability. Given some specified long-shunt and short-shunt compensation capacitances, the voltage regulations with the generator connected to purely resistive loads and inductive loads, respectively are evaluated, which shows that the long-shunt and short-shunt connection capacitors not only modify the external characteristics of an induction generator but also increase its ability to carry loads. The importance of selecting suitable capacitances for voltage compensation is also emphasized in the paper. For different terminal capacitances, the external characteristics of an induction generator with purely resistive load and inductive load, respectively, are obtained, which follows that the shunt compensation capacitors can also increase its ability to carry load. The optimal occasion for putting the shunt compensation capacitor is also determined by comparing the maximum voltage regulation before the capacitor connection with that after the capacitor connection.The establishment of stator voltage is the basis of the steady-state operation and the determination of the self-excited capacitors is the key point. A direct search method presented by Hooke-Jeeves is utilized to solve constrained optimization problem that offers the advantages over those of Newton-Raphson method in stability and flexibility. With the calculated capacitance, a given no-load terminal voltage is build up.