Integrator windup

30.03.2010 21:08

I'm playing with a thyristor regulator proof-of-concept circuit for my lab power supply. Right now I'm using an op-amp integrator in the feedback control loop and I stumbled upon this nice example of how integrator windup can screw up a control system's response.

Simple feedback control loop

Image by en:User:Ap CC BY-SA 3.0

The upper, blue trace shows the output voltage (plant output y in the block diagram above). The lower, orange trace shows the integrator output (u). The orange shaded area shows where the plant is roughly linear - when integrator output is outside those bounds, the thyristor control circuit is in saturation and the output won't change much.

This is the response of the system to a negative step in the setpoint, without any special measures:

Negative step response with ringing due to integrator windup.

And this is the response to the same input with the integrator output limited by a Zener diode:

Negative step response with limited integrator output.

And finally, just to show off, here are both positive and negative step responses on the same picture:

Two step responses of a thyristor regulator.

I'm more interested in optimizing the positive response, since that's what will be important here. The output will be regulated by a linear regulator which can take a moment of excessive power dissipation due to overvoltage, but it can't correct for an input voltage that's too low.

The delay after the step response is 30 ms, while the theoretical minimum would be 10 ms. I doubt I'll be able to get it much lower without compromising stability.

Now I just have to figure out how this model will scale up to the real thing.

Posted by Tomaž | Categories: Analog

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