Quote:
Originally Posted by P-hack
So, boost inductors of low inductance value like large currents to stay out of discontinuous mode. And a boost isn't technically needed for a v/hz below battery voltage, but I don't know how hard that makes the inverter controllers job having multiple bus voltages. But a smaller value inductor for a given current carrying capacity will mean less losses.
For most of my driving, I pulse and glide, so an all-or-nothing booster would be quite manageable, but with a cpu it could do that on a much smaller scale, i.e. run the booster %10 of the time, or 10/100 of a second or more depending on demand to optimize the inductor to the smallest "continuous boost mode" size. Is that sort of what you are thinking CTS? I would like to see it rated for continuous duty cycle though, direct drive vehicles will need boost for sustained high speed.
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Correct. But in practice higher inductance is better as it allows continuous current down to a few amps and a very low ripple while under heavy use. It also allows a smaller igbt peak current. Lower inductance is best for small size, but the penalty is reduced efficiency at low loads.
The losses are proportional to the ripple. So while a larger inductor has a higher resistance, it has less core losses and vice versa. One has to find a compromise and needs to have in account the
average current, rather than the
peak current. I'm cool with having 200Amps output, but how many
seconds will I use the inductor at these levels during a charge cycle? So I would say the sweet spot on efficiency should be calculated to match the motor nominal power. On a 18HP at 208V that would be less than 70Amps. And let me mention, if I haven't, that the gains are larger should the output be boosted to 450V at 70Amps that to 300v at 150Amps. In fact the sweet spot for a 208V 4 Pole motor is sqroot(2)*415 = nearly 600V for full torque up to 2900RPM and of course, at such power levels the motor would have 36HP nominal with no loss of performance or operational time limits other than the battery running out!
Continuous boost is needed for high speed, correct. But not at 200Amps. Say 70-90Amps, which would draw ~ 200Amps from the battery (40HP). If the motor only has a duty cycle of 15 seconds above this, it doesn't seem right to design a boost converter which is any different.