Originally Posted by
waterfalls123
So how is an aircraft electrical system like the 787 able to be powered by these large, variable frequency AC generators without a constant speed drive (CSD)? My understandings of AC electrics was that motors driven by AC power need stable frequency in order to operate properly and for longevity. Why do "relatively" modern aircraft like the 777 bother with the weight of complexity of constant speed drives (CSDs) and an aircraft like the 787 doesn't need CSDs?
The 787 uses 'VSCF" - Variable Speed, Constant Frequency. In short, the VSCF uses electronics to convert the output to a constant frequency. So they do electrically what the CSD does mechanically. So the aircraft systems don't need to deal with the wild frequency outputs.
The 777 also uses VSCF - but much lower power output (20 KVA on each engine, if memory serves) for 'backup power', as compared to the 150 KVA output of the constant speed IDG.