why does the PI controller not give an output when its inputs are gotten from a calculated value rather than a gen?

I have a model Which compares the speed of a generator with a reference speed and sends the error through a PI controller. When I get the speed from the gen itself, the controller works fine but when I perform some calculations to get thethe same speed value from the line voltage and current, the PI controller does not give an output. I have tried using a unit delay, zero order hold and it still doesn't work. Why does the PI controller not give an output when the input error is calculated instead of gotten from d gen? Please help

Answer 1

[Dennie]

The information provided is rather limited, but I'm assuming that you removed the generator from your loop and replaced it with a constant value. This will result in an error for your PI controller, which is normal. However, the PI controller integrates the error to remove the steady state error introduced by the high gain feedback loop. Assuming you are not running your simulation in real-time, the integrated value will become very high very quickly, which can result in simulation errors. This does not happen for the generator model, because the Pi controller can actually influence the speed and reduce the error to zero.

Hope this helps, Dennie