Re: [EVDL] EV controllers- controlling both voltage and current
Phil Marino wrote:
> I agree with Morgan that you can't control current and
> voltage independently in a series motor. What I mean
> is that you can't arbitrarily apply a desired voltage
> and a desired current at the same time.
> But, you can certainly limit both, as you suggest. I
> don't think this is what he meant, though.
Well, I'm not sure what he meant, but I'd hope that if he is halfway
through an EE program he has encountered and understands Ohm's law!
Since it isn't possible to force an arbitrary current to flow through
*any* given impedance (motor, resistor, etc.) while forcing some
unrelated arbitrary voltage across it I wouldn't expect that to be what
he was asking. ;^>
The *only* thing he could do that resembles what he asked about is to
have independent control over the controller output voltage and current.
As he increases the voltage (limit), the current will increase (in a way
defined by the impedance of the load) until it reaches the present
current limit. If he continues to increase the voltage command/limit
without adjusting the current limit, the current remains fixed and the
voltage increases as the motor speed increases (since the motor is a
load whose impedance varies with RPM). If he turns up the current
limit, then the current increases until it reaches the new limit, or the
until the voltage bumps up against the present voltage limit, and so on.
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