Design of four-switch STATCOM for voltage control of wind-driven squirrel cage induction generator

This paper presents an isolated three-phase induction generator (IG) with fixed frequency and controllable output voltage using a three-phase four-switch Static Synchronous Compensator (STATCOM) with space vector modulation (SVM) switching method. A squirrel-cage three-phase induction machine is used with two separate windings on the stator by a star connection. One of the machine three-phase windings is used as the excited winding and the other is used as the power winding (main). Because of the magnetic coupling between two windings, to prevent the transmission of the active power from the excited winding to the power one the three-phase STATCOM is controlled in a closed-loop circuit. Thus, it would just inject the reactive power needed for the machine to the excited winding. In order to control the real power oscillations resultant of the load and wind speed oscillations, it has been used of the blade pitch angle control, which is modeled composing the whole generator system. One of the prominent features of this generator, in contrast to the other isolated IGs, is its fixed frequency and its independency from the machine mechanical driver speed. Moreover, its output voltage is well controllable.