Frequency converter apparatus

Claim 1

Apparatus for varying the frequency of a-c power supplied to a load comprising: a first rotating alternating current machine comprising a stator and rotor windings, the rotor windings being electrically connected with the load; a second rotating alternating current machine comprising stator and rotor windings connected with, and for rotatively driving, said first machine; a distribution network providing a source of a-c power of fixed frequency to the stator windings of both said first and second machines; and a control network for increasing the rate of rotation of said second machine in one direction, thereby to increase the frequency of the a-c power supplied to the load above said fixed frequency, and for rotating said second machine in the opposite direction, thereby to decrease the frequency of the a-c power supplied to the load below said fixed frequency, said control network comprising: at least one variable impedance saturable core reactor electrically interconnected with the rotor windings of said second machine, the a-c impedance of the reactor varying in response to both the magnitude and the polarity of a d-c voltage across the control winding of said at least one saturable core reactor, and means for varying both the magnitude and the polarity of the d-c voltage across said control winding.