Abstract: A dynamoelectric machine having a multiple of three poles and a corresponding multiple of three brushes is disclosed. Each of the poles are wound poles, two of each group of three poles being excited with a constant excitation during normal operation, the third of each group of poles being a control pole, excited so as to produce a flux that both varies in magnitude and reverses in polarity. With an input voltage connected to first and second brushes of each group of three, an output voltage may be derived from first and third brushes in a magnitude determined by the polarity and intensity of the field of the control pole. The machine is also adapted to provide mechanical output power from its rotating shaft, and also to accept input power from its rotating shaft. The output voltage obtainable may be varied between zero and the value of the input voltage, and also increased above the input voltage, and decreased below zero, reversing polarity.