peskanov wrote: Coulomb,
when manufacturers rate the amps of an AC controller, are they talking about 3-phase current or battery DC current?
My understanding is that they usually specify the RMS current per phase at the output.
It turns out that when the controller is at maximum voltage, then the voltage at the output is about 1/sqrt(2) of the input DC voltage. The power output is (line voltage) x (line current) x (sqrt(3)), which is then about (DC volts / sqrt(2) x (RMS output per phase) x sqrt(3). Neglecting inefficiency and power factor, the input DC bus current (RMS) is therefore the above divided by (DC volts). So the input current is about sqrt(3) / sqrt(2) higher than the output RMS per phase current. Power factor is typically around 0.85, and the pack doesn't supply reactive power (only its losses), so the input current is typically around 1.73 / 1.41 * 0.85 times the output current per phase, or about 1.04x the output current.
Hence most people make the approximation that the DC input current (at maximum output voltage, usually at base speed or above) is the same as the RMS output current per phase, or a tiny bit more. In other words, an 800 amp AC controller is much like an 800 amp DC controller, drawing up to 800 A at maximum power.
As with a DC controller, at lower speeds the voltage will be lower, so at startup 800 A can be generated while only drawing say 200 A from the pack (depending on many factors).
I assume that they usually specify the output RMS per phase current, as that is the limit set by the IGBTs or MOSFETs, but the input current depends on many factors, including characteristics of the motor.
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