A solid state power transformer is described for converting an input power signal at a first phase or voltage to an output signal of a second voltage or opposite phase by the use of bidirectional solid state switches switched at a high carrier frequency to produce a double-sideband, suppressed-carrier representation of the input power signal, which is then synchronously demodulated using further similar switches to produce the desired output. It is further disclosed that multiple instances of the above with relative phase-staggering of the switching frequency may be operated in parallel and activated or deactivated according to output current demand to provide maximum efficiency over a wide range of current and power levels.