Automatic Generation Control (AGC) (Con td..)

An integral controller acts on this error to change the load reference of both governors. Since an integral controller drives its input to zero in steady state (why?), it follows that in steady state:

which means that in steady state, both frequency deviation and tie line power flow deviation are made to go to zero by the AGC.

While any value of the weighting factors which are non-zero gives the same result in steady state, they are chosen such that the transient response is good.

We illustrate this concept on the same system as in the previous example.