In the past, small-scale renewable generation relied on tried and proven induction generators. The problem with conventional induction generators is that they cannot generate reactive power, required for connection to larger grid systems. This article describes an answer to this problem - doubly fed induction generators, also known as DFIG machines. DFIG machines are based on the induction generator but have a second winding, either on the rotor or the stator. This is fed by an electronically produced variable frequency source, so that the output of the generator can be controlled with regard to both frequency and power factor. As a result the DFIG can capture energy over a wider range of wind (rotor) velocities, boosting its output and efficiency. Reactive power can also be absorbed and generated according to the load or grid requirements to which the DFIG is connected. As a practical example, a brushless DFIG is described in detail.