EHA Loading on the 270-Vdc Bus

The Power-by-Wire (PBW) aircraft is quickly becoming a reality. The recent developments in the area of electrically driven actuators for primary flight control surfaces are showing that this technology is viable for the next-generation fighter aircraft. The architecture for the PBW aircraft is considered to be a 270-Vdc redundant (quad or triplex) distributed power bus with isolated avionics buses. One of the major considerations in the design of the Aircraft Generating System (AGS) is the loading on the AGS during transient operation of the actuators. More specifically, there is concern that the AGS will not be able to supply the necessary current to accelerate the surface inertia at the high slew rates required by the aircraft performance envelope. That this is not a concern is shown by the analysis and testing performed on the development 24-hp Electrohydrostatic (EHA) system at GE. The analysis is performed on one of the 12-hp motors that drives a dual-tandem actuator. The analysis is based on the fact that the AGS, since it is dc, can only supply real power, and real power is developed only when there is rate as well as hinge moment. During the initial acceleration of the surface, the real power is low and demand on the bus is low. As the rate increases, the torque demand fails off and the bus supplies the power required. The analysis is verified by testing.