US Patent 9273610 Starter/generator combination with all variable frequency drives

A gas turbine engine includes a compressor, a combustor adjacent the compressor, a turbine adjacent the combustor, a shaft, a motor, a primary variable frequency drive, an auxiliary variable frequency drive, and an auxiliary motor. The motor is coupled to the shaft. The primary variable frequency drive is electrically connected to the motor and an AC power source. The auxiliary variable frequency drive is electrically connected to the primary frequency drive. The auxiliary motor is electrically connected to the auxiliary variable frequency drive.