Multi-phase power supplies

Claim 1

Apparatus for converting an alternating current power supply having a single phase of given period to a power supply having a plurality of phases, said apparatus comprising an electrical bridge network having an input connected to said single phase, an output, and four arms each of which contains at least one switch device, and external switch circuitry for controlling the said switch devices, the four arms of said bridge network comprising two pairs of opposite arms each of which is selectively capable of forming a conducting path between said input and said output under the control of said external switch circuitry, said external switch circuitry being operative to switch the switch devices contained in each pair of opposite arms from a nonconducting state to a conducting state and from a conducting state to a nonconducting state at least once during every half period of said single phase to provide at said output a voltage waveform which contains a fundamental component of the said single phase which is out of phase with the single phase by a predetermined phase angle.