Computer Simulation of a Series-Connected Induction Generator and Determination of Minimum Required Capacitance for Self-Excitation for Wind Energy Applications

A series-connected induction machine is obtained when the stator and rotor windings of a conventional three-phase wound-rotor induction machine are connected in series but with opposite phase sequence. For this machine to become self-excited, the machine terminals must be connected in parallel with a three-phase capacitor bank. In this paper, Direct-Quadrature (D-Q) theory and space vectors are applied to investigate the performance of a series-connected induction machine operating as a standalone generator as in a wind-turbine application, for example. Accurate models of the generator are derived at no-load and with resistive and resistive-inductive loads. The minimum capacitance for self-excitation at a constant speed is also obtained at no-load and at a loaded condition. Numerical simulations predict the generator output voltage as a function of the amount of capacitance at the machine terminals during steady-state operation.