Quote:
Originally Posted by harlequin2
Really, you shouldn't even consider IGBTs unless you are planning on driving an induction motor. Or perhaps a brushless dc motor.
Series wound dc motors such as are commonly used in EV conversions (Netgain, Advanced DC, etc) don't need voltages higher than 150 - 170 to achieve full speed and 200V FETs are quite happy at those levels. You do need the higher voltages for induction motors though as the higher inductances mean higher back emf and hence more volts are needed to push the current through the windings.
FETs are generally easier to drive than IGBTs and they don't mind being paralleled as much either. They also have lower losses - usually - because their on resistance is less. Switching times are much the same, so switching losses are similar.
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as stated before, the reason for going with igbt's and higher voltage would be for efficiency purposes. right now, from what i've read, it looks like the mosfets in most motor controllers are dumping around 50 watts of heat each. multiply this by 12 or so, and that's 600 watts of energy that's being used to warm your motor controller instead of drive your wheels (or track.) From everything i've read, all of the switching devices (mosfets and igbt's) are more efficient at lower currents. because of this, the plan is to run 3 igbt's in parallel (which, from the data sheets i've read, is completely possible if you follow strict procedure to make sure they are all mounted to the same heatsink and are of the NPT type.)
This will keep current through each igbt down to around 50 amps during normal "cruising" operation and keep Vce down to around a volt. lower Vce, lower conducting losses.
Paul, do you know where i can find the igbt driver schematic or board on here? i did a quick search and didn't find it right off.