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Old 11-23-2015, 08:29 PM   #2357 (permalink)
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Originally Posted by e*clipse View Post
Notice the circuit has no capacitor and no inductor. There's no energy storage capability in that circuit.
it is used to model the current ratio of the inverter switches vs the boost converter switch. The storage is irrelevant in this example, as a capacitor blocks dc. Using sinewave currents to model the motor windings is just a good approximation. If your motor currents aren't reasonably sinusoidal, then you are doing something wrong.

The only thing a capacitor would do here (if it is large enough) is stabilize the dc-link voltage at about 100v, the D1 current is still going to be about 3x what an inverter switch would see on average.

Sometimes it helps to break down a problem into it's component parts for analysis though. Designing a whole car in ltspice can be challenging, I can't even do 3 sine current sources in wye (though I wonder if anyone can), but as long as the phase currents are right, no matter for our switch sizing purposes.

If you are wondering what the waveforms look like for a typical boost converter (with downstream storage), I attempted to model pauls 50 lb ch-200 a bit here. output is again about 100v (108) and load current is also, so this would drive the hypothetical motor in the previous diagram. These particular diodes are having lots of recovery issues.
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