Piotrsko:
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Over on the DIYelectric site someone was commenting about some motor (honda?) has an inverter that doubled battery voltage to 500, so I would bet that 750 isn't unreasonable.
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Toyota boosts their hybrid's battery pack to a DC Bus voltage of 500, for increased efficiency of the IPM motor at high RPM's. Apparently the efficiency gain and/or battery pack cost reduction is more than enough to offset the additional losses from the bidirectional DC-DC buck/boost converter between the DC Bus and the battery pack.
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I still cant figure out a separation scheme for series batteries. based on my experiences, it is hard to not get full voltage leakage to somewhere. and high voltage high current stuff is $$$$$.
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I don't discount that you've seen it, I just can't figure out how it happens. Note that I'm an ME, not an EE, so I may be looking at it all wrong. I know of things like capacative and inductive coupling, but don't really understand them. Any other sort of "leakage" I can think of implies a degraded or bypassed or otherwise faulty insulator. I'm having trouble figuring out how one can get full voltage leakage (or any voltage, for that matter) without at least two insulation faults in the otherwise isolated HV system. This isn't like the AC system in a building, where any voltage is *relative to earth ground* by design - so poke a wire at your peril. In an isolated EV HV system, that is not currently plugged into a charger, all points in the system should have zero volts *relative to earth ground*.
I guess it boils down to, which costs more: engineering a safe 720-800VDC EV system to raise the power of a single motor without excessive current/heating, or running dual motors to share the current at 360-400VDC - whether they parallel off a single inverter or have to use two separate ones. Either way, I hope to beat the ~$9550 for a 123kw peak/~56kw continuous output HPEVS system, consisting of an oil-cooled AC-35x2 (basically two AC-35 stators in one housing with two rotors on a common shaft) motor and dual water-cooled Curtis 144V/500A controllers. (oil pan 4 - this is the sealed regen-capable off-the-shelf solution I am trying to beat.) One Nissan Leaf motor can get me 80kW continuous - we don't know peak yet.