the output of the boost converter that is filtered by capacitor 28 enters the six step voltage source inverter 83 which comprises three pairs of transistor diodes 44 49 in parallel the energy is stored in the boost inductor 34 by turning 34 on 34 both transistors 35 and 36 during this period the six step voltage source inverter 83 is supplied by the energy stored in the capacitor 28 the energy stored in the boost inductor is delivered to load by turning 34 on 34 transistors 35 or 36 alternatively followed by the energy storage cycle of the boost inductor the secondary output of the transformer 37 is rectified by the full wave bridge rectifier 38 and fed to the six step inverter 83 the boost converter 82 is controlled by the pulse width modulation controller 90 the speed torque characteristics of the apu engine to be started is such that the drag torque increases with speed up to the engine light off and the engine provides torque assist after light off only about 20 25 of the rating of the generator power is required to start the apu engine and constant power operation mode provides sufficient torque to overcome the engine drag torque and accelerate the engine to the rated speed within allowable time constant input power operation mode has been selected as the starter generator develops sufficient torque to overcome drag torque and.