Introducing integral control action in the governor creates an additional real pole
near the origin, related with the slow elimination of the frequency error in the steady
state. Increasing the integral gain, Ki, accelerates the response of the system but
reduces considerably the damping of its dominant poles, resulting thus in strong
oscillations in the response and a reduced stability margin. A Ki value between 4
and 5 p.u. represents the best compromise for the system considered in this paper.
In Fig. 8, the frequency of the system is plotted for a 0.2 p.u. step load increase.
The governor parameters are set to R=5% and Ki=4. The response is quite oscillatory,
but an increase of the droop in order to provide extra damping would create an even
larger maximum frequency excursion. Reducing the integral gain Ki, on the other
hand, would increase the restoration time of the frequency, without significantly
improving its damping.