DC Link VSCF Starter/Generator Systems

The double duty function of a starter/generator system offers the aircraft industry the possibility of a lighter weight airplane and the capability for direct electric start of the engine. The electric start system will also permit sustained motoring of the engine for ground maintenance or de-flooding procedures. Power to drive the starter in the form of three phase, 115vac is furnished by the on-board APU, the external power unit, another aircraft's electrical system or by another generator on a multi-engine aircraft. The DC Link starting system draws current from the power source which is small at the beginning of the start cycle and increases as the engine RPM builds. This feature allows other loads to remain on the AC bus during engine starts. This paper elaborates on these advantages and presents the latest concepts and test results for such systems. A time to start computer simulation was developed which is used to help the airframe manufacturer determine the best system rating and evaluate special torque/speed profiles for the starter to optimize the overall system design.