Drunkskunk wrote: ↑
Jun 23, 2014 6:23 pm
But Phase A is up, is relying on Phase B and then C for ground. With a Sinus wave form, you never get a good ground, you're almost always in transition. That might be fine for reducing noise, but it means the Dropping phase is still falling through the transition of both the other phases, and that can't be good for efficiency or power delivery.
I think you've got that a bit backwards.
"Sine wave drive," although it's somewhat new for ebikes, has been used since the first electric motors came out. One of the characteristics of a three phase sinewave motor drive is that the vector current is always the same; the motor always sees the same field. Compare that to a square wave drive where there are hard transitions where the motor current drops out then returns.
Driving all three phases is referred to as 180 degree modulation.
Both square wave drives and sine wave drives offset each phase by 120 degrees.
not sure how it affects efficiency, but i found it interesting andrey said at 41:16, "when you use sine wave, you use all three windings at the same time. if you use block controller, at one time you use only two windings.
Sort of. In a delta wound motor, when the voltage between phases A and B is the same, you don't see any current in that phase (or more accurately no induced change in current, which is what's important.) In a sine wave drive that happens periodically but lasts a short time since the phase relationship is always changing. In a square wave drive that lasts a longer time. However, in a wye wound motor that's not true, since current will keep flowing through all three windings even when A and B are at zero volts and C is at battery voltage.
Also, the above is very oversimplified, since back EMF keeps voltage changing (and current flowing) through all three phases constantly.