US Patent 7254465 No-break-power-transfer control system for variable frequency electrical power systems

A method and apparatus for executing a no-break power transfer between an electrical power generator powered by an auxiliary power unit (APU) and an electrical power generator powered by an aircraft main engine. The method comprises sending a power transfer command, a load/unload amplitude signal, and a target frequency signal from a bus power control unit to an APU electronic control unit; deriving a calculated load range for the APU at a new load and frequency operating point; and determining if the new load and frequency operating point falls within the calculated APU load range. If within range, a no-break power transfer is initiated; if not within range, a power transfer with momentary interruption is initiated.