Abstract: The electrical supply system on aircraft may employ a constant speed drive (CSD) to convert variable engine speed to constant speed for operation of synchronous 400 Hz electrical generators. The heart of these devices is a differential which mechanically sums the input of two shafts and outputs this sum to a third shaft. Connected to this third shaft is a constant speed synchronous generator. Connected to one of the input shafts is the turbine generator (most likely through gearing). The second input shaft is connected to a speed compensating drive which accounts for engine speed changes. The speed compensating device disclosed herein is an electrically compensating motor/generator arrangement. Bidirectional power flow in the electric compensation link uses two high-speed, permanent-magnet, three-phase machines interconnected by a power conditioning network. One machine is operated as a brushless dc machine, while the other functions as a variable speed synchronous machine.