Steady state analysis of a doubly-fed induction generator under synchronous operation

A detailed analysis of the performance of the doubly-fed induction generator (DFG) under synchronous operating condition in the steady state is presented. The rotor is excited by a voltage phasor, the magnitude and the frequency of which can vary independently. The frequency supplied always has such a value that, if superimposed on the rotor speed, a synchronous rotating field results. This produces variable-speed constant-frequency characteristics of the DFG over a wide speed range. By varying the excitation voltage magnitude the stator and rotor power factor can be controlled so that maximum efficiency can be achieved. By varying the angle between the stator and the rotor applied voltages, the DFG active power delivered can be controlled. The wide range of variable-speed constant-frequency operation and the capability of load variation and power factor control makes the DFG attractive for wind power conversion systems as well as variable-speed hydroelectric generators