US Patent 9045996 Gas turbine engine optimization by electric power transfer

A method of increasing the operational efficiency of an operating gas turbine engine includes supplying mechanical power from a first spool of the operating gas turbine engine to a first electrical machine to thereby generate electrical power using the first electrical machine and supplying mechanical power from a second spool of the operating gas turbine engine to a second electrical machine to thereby generate electrical power using the second electrical machine. The method further includes sensing one or more operational parameters of the operating gas turbine engine and, based on the one or more sensed operational parameters, ceasing to generate electrical power using the second electrical machine, and instead supplying at least a part of the electrical power generated by the first electrical machine to the second electrical machine to operate in motoring mode and to thereby generate and supply mechanical output power to the second spool of the engine.