|
IF the power loss across an IGBT is LESS than the power loss across a freewheel diode, then the gain from syn.rec. comes during the "off" portion of the PWM and is relative to the current...
Basically, when the driving switch (mosfet bank or igbt) is off, the current still has to flow somewhere (because the motor is a huge inductor), so there is a freewheel diode in there. Typically a mosfet bank will have a lower Vdrop then a diode, so when you turn off the driving switch, you turn on a mosfet in place of the diode. That's sync rec. So if you are pushing huge current, you get huge gains in efficiency.
If you want to K.I.S.S, then just use a freewheel diode and account for the heat.
|