Some times PID control is not enough, and it is necesary to improve the control. One posibilty is using a two degree of freedom controller. In this approach a prefilter is used in the reference input to improve the controller response.
I suggest to read:
[Skogestad, Postlethwaite, 1996] S. Skogestad., I. Postlethwaite. "Multivariable Feedback Control" . John Wiley & Sons, Baffins Lane, Chichester, 1996
So im working on automatic generation control of a 2-area power system. anyone have any ideas as to how i go about determining the values for the PID controller to achieve load frequency control. thanks