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Old 11-09-2009, 08:19 PM   #36 (permalink)
NiHaoMike
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One problem I have thought about was the high voltage requirements if a common industrial motor is used. A higher voltage battery can be used, although that would increase costs, or a boost converter can be added just like in the Prius. But a friend of mine already thought of that problem. (She sure is smart! Too bad she says she is "self sufficient"...)
high current inductors from copper tubing? - diyAudio
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One problem is that most industrial motors operate at 208-230v minimum (for rated power), which translates into 300-325v plus overhead of DC. Not exactly practical for a battery pack. But to step up a 180v battery to 400v with a maximum load current of 200A (translates into about 100HP) at an operating frequency of 15kHz only requires about 16.5uH. That is practical for a copper tubing inductor cooled with oil. One major problem is that the metal of the car would act as a shorted turn. However, hypermilers often add "Kammbacks" to their cars. If the Kammback is made from a nonconductive material, the inductor can be installed inside it in such a way that the metal would be far away enough to not cause problems. I'm not sure about heat dissipation of 1/4" tubing when conducting 200A, but I would not expect it to be a problem as the load would usually be much less, maybe as low as 15A when cruising.
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And I realized that since it would need to be a bidirectional converter in order to be able to regen, there would be no need for a separate charger buck converter. Simply rectify mains voltage (using a voltage doubler for 120v) to the boosted rail and run the converter as a buck converter to charge the batteries. In a DIY EV where cost is a major concern, it can be very helpful for saving cost.
So add a plastic boattail to improve aerodynamics and house the coil for the bidirectional boost converter, then add a rectifier so it doubles as a charger. Since the components would be rated for very high current, it would work great for a fast charge. And you'll be able to get more voltage to run common industrial motors. Three birds for one stone!

Also note that since higher voltages are only needed for high speed, the boost converter can be disabled until the car is up to speed and more voltage is called for, at which point the boost converter activates to get just enough voltage. (The Prius boost converter is dynamically controlled in that manner.) During regen, the boost converter is reversed to operate as a buck converter. The real beauty is that with IGBTs, the integrated reverse rectifier has a fast recovery time (unlike MOSFETs) so you don't need to manually turn on the commutating IGBT. (IGBTs also cannot conduct in reverse so that would be pointless anyways.) So when the boosted rail needs to be increased, start switching the low side IGBT and when it needs to be lowered, start switching the high side IGBT, leaving both off by default.

what is carrier freq in VFD?
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For industrial applications where efficiency is far more important than - slight - noise levels, carrier frequencies of 1 - 4 KHz are normal.
So the inverter should operate at low frequencies to reduce switching losses, but the boost converter should operate at higher frequencies to reduce the size of components.
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