Polyphase alternating current frequency variator for induction and synchronous type motor

Claim 1

A frequency variator which includes input terminals adapted for connection to a polyphase alternating current supply and corresponding in number to the number of supply phases; a pair of output terminals for each of a plurality of load phases and adapted for connection to opposing ends of a load phase; a plurality of power control gates for each output terminal and corresponding in number to the number of supply phases, the output ends of the said power control gates for each load phase being connected to the respective output terminals, the input ends of the said power control gates being connected to the respective input terminals, and the said power control gates being adapted to permit alternating current power to flow through them in the form of pulses when triggered to do so; and control means adapted to control the rate and sequence of the triggering of the power control gates to permit them to pass alternating current power in the form of pulses in cyclic ordered sequence from any input terminal to any output terminal, the control means including: a. a variable frequency means for varying the rate of triggering of the power control gates; and b. synchronizing pulse means for preventing backfiring between supply phases via power control gates connected to the same output terminal, by controlling the triggering of such power control gates and thereby preventing them from becoming conductive simultaneously.

Claim 3

A method of varying the speed of polyphase alternating current induction and synchronous type motors having a plurality of phase windings and energized from a polyphase alternating current power supply which includes sequentially switching alternating current power pulses in cyclic ordered sequence from every supply phase to both ends of each phase winding, varying the frequency of said pulses to the said ends of the phase windings to set the speed of said motor at a desired rate of rotation, and applying natural commutation to said pluses switched to said phase windings in order to prevent backfiring between phases so that a pulse from a particular supply phase is not applied to any one phase winding until a pulse from a different supply phase applied to that phase winding has terminated.

Claim 4

A method of varying the speed of polyphase alternating current induction and synchronous type motors having a plurality of phase windings and energized from a polyphase alternating current power supply which includes sequentially switching alternating current power pulses in cyclic ordered sequence from every supply phase to both ends of each phase winding, varying the frequency of said pulses to the said ends of the phase windings to set the speed of said motor at a desired rate of rotation, and applying natural commutation to said pluses switched to said phase windings in order to prevent backfiring between phases so that a pulse from a particular supply phase is not applied to any one phase winding until a pulse from a different supply phase applied to that phase winding has terminated.