Lockheed Martin Corporation

Michael Francis Thompson

William Anders Peterson

A polyphase AC-to-AC inverter (300) for driving a polyphase load (50), which may be an unbalanced load, includes a wye-connected AC voltage source (12) having a neutral terminal (312). The source (12) is coupled to a rectifying arrangement (16) for producing direct voltage across a direct-voltage bus (22). A capacitive bridge (24) on the DC bus (22) has a tap (26) connected to the neutral (312) of the source. The capacitive bridge is isolated from the AC source harmonics by a zero sequence inductor (20). The DC bus voltage at the capacitive bridge feeds a polyphase switching bridge (40). The average voltage at the output of the switching bridge is recovered by a low-pass filter (30) connected to the load. The unbalanced load current is conducted through an inductor to the capacitive bridge tap and the source neutral, with the inductor impedance isolating the load neutral from the DC bus. The switching bridge control can introduce triplen harmonics in the output to increase line-to-line output voltage.

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Michael Francis Thompson