Patent ID: 7274547

Claim:
An electric power supply system comprising: a source of AC power which is operable to provide an AC output voltage; a series train AC/AC conversion circuit comprising a first converter operable to establish an intermediate DC link by converting the AC output voltage into an intermediate DC voltage and a second converter operable to convert the intermediate DC voltage into an AC output voltage for supply to an external load; a bypass circuit which connects the AC output voltage provided by said source directly to the AC output voltage of the second converter thereby bypassing the series train AC/AC conversion circuit, the bypass circuit including an electronically operable unidirectional switch arrangement for the AC output voltage provided by said source, the electronically operable unidirectional switch arrangement being operable to enable current flow through the bypass circuit as well as through the series train AC/AC conversion circuit when the power supply system is connected to an external load; a current sensor operable to sense output current flow from the series train AC/AC conversion circuit when the power supply system is connected to said load; and a control unit responsive to said current sensor and operable to control said unidirectional switch arrangement and thereby to control current flow through said bypass circuit, wherein a trip switch is provided for the AC output voltage of said second converter and said bypass circuit, said unidirectional switch arrangement being open normally so that normally there is no current flow through said bypass circuit and said control unit being operable to close said unidirectional switch arrangement in response to said current sensor sensing current flow through said series train AC/AC conversion circuit in excess of a predetermined current for a predetermined time so that the flow of current from said series train AC/AC conversion circuit to said external load through said trip switch is augmented by current flow through said bypass circuit whereby the switch is caused to trip by the augmented current flow through it.