Ageneral phasor transformation theory for analyzing all linear ac converters such as inverters, rectifiers, cycloconverters, and resonant converters is suggested by unifying the circuit D-Q transformation for polyphase ac converters and the phasor transformation for single-phase ac converters. The system order of polyphase ac converters is degenerated to that of single-phase converters, and the switches in all ac converters, regardless of the numbers of switches and poles, are replaced with an equivalent transformer with a complex turn-ratio. The analysis of ac converters is drastically simplified by the proposed circuit-oriented approach.