Electronics > Beginners
Advises on programming/tuning a PID for Peltier element
Kleinstein:
The driver shown is made to work with a motor and does output just a relatively slow PWM. This is not really good for driving a Pletier element.
It gets especially bad if the peak current is more than about half the nominal current. At high currents and low frequency PWM drive also reduces the life of the Peltier element due to thermal stress.
For a relatively slow control one can get away without the derivative term. If it has to be relatively fast (compared to the system) one does need the derivative term. However this requires a reasonably good set of parameters. With just 2 parameter in the PI regulator one might still find a good solution by try and error. It's much more difficult in the PID case.
A Peltier element is a nonlinear control element. One one gets closer to the maximum current it gets quite nonlinear.
For fast and accurate regulation over a larger range, it might be worth to include this nonlinear (but know relatively simple formula) relationship. So the PID would calculate the required power and a second step would be to calculate the required current from the desired power.
Ideally one would also include the other side temperature as a kind of feed forward or a little simpler (because no extra parameters needed) as a part of the formula to calculate the required current.
Momchilo:
I never tried to control the temperature of a Peltier element. But I think it's necessary to have two PI-controllers in a cascade. The D-part isn't important.
One controller (inner loop) for the current and the outer controller for the temperature. The output of the outer controller is the setpoint of the current controller. The current controller should be much faster than the temperature controller, because you can change the current immediately, but the temp only very slowly.
It's very similar to a speed control of a dc motor.
But I don't know, if that's the best way.
Kleinstein:
There is usually no need for an extra digital cascade control. The output stages are usually reasonably well behaved, so that one can pretty much predict the current from the set value. If at all this could be done linear, as a kind of current controlling amplifier.
arronar:
--- Quote ---The driver shown is made to work with a motor and does output just a relatively slow PWM. This is not really good for driving a Pletier element.
--- End quote ---
So, then which is a good driver/way to drive a Peltier?
chemelec:
I use Mosfets to turn them on and Off.
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