Generalised LFC model

When renewable power plants are introduced into the power system, an additional source of variation is added to the already variable nature of the system. To analyse the additional variation caused by RES units, the total effect is important, and every change in RES power output does not need to be matched one for one by a change in another generating unit moving in the opposite direction.

Instantaneous fluctuations in load and RES power output might amplify each other, might be completely unrelated to each other, or may cancel each other out. However, the slow RES power fluctuation dynamics and total average power variation negatively contribute to the power imbalance and frequency deviation, which should be taken into account in the LFC control scheme. This power fluctuation must be included in the conventional LFC structure.

In typical LFC implementations, the system frequency gradient and ACE signal must be filtered to remove noise effects before use. The ACE signal then is often applied to a proportional integral (PI) control block. Control dead band and ramping rate are different for various systems. The control can send higher/lower pulses to generating plants if its ACE signal exceeds a standard limit.