A novel variable speed cage induction generator

This paper presents a novel technique to generate power at constant frequency using a 3-phase cage induction motor, operated under variable speed conditions and without an intermediate inverter stage. The technique uses any one of the three stator windings of the motor as the excitation winding, and the remaining two windings, connected in series, as the power winding. The proposed two series-connected and one isolated (TSCAOI) winding configuration cancels out the mutual coupling between the excitation winding and the two windings connected in series, making them magnetically decoupled for independent control. Power is generated through the series connected two windings with appropriate excitation to the single winding at desired frequency when the rotor is driven either by a wind or hydro-turbine at variable speed. Either a simple single-phase squarewave inverter or a reversible rectifier can be used to excite the single winding at the desired frequency of generation. Simulations are presented to prove the validity of the proposed technique, which is simple and requires no output filtering for grid-integration as harmonics from excitation inverter are filtered-out by the generator itself.