Page 257 - Mathematical Models and Algorithms for Power System Optimization

Optimization Method for Load Frequency Feed Forward Control 249

where ϕ∗ is given by the load model. The system can be controlled based upon the forecasting
values of load disturbance ΔP L .

7.6 Load Frequency Controller of the Power System

As previously discussed, the power system load frequency controller is of an integral and state
feedback type. Here with the invariance principle, a new discrete compensation controller is set
up, which is suitable for the digital machine control to compensate the system load disturbance
and control the system state.

7.6.1 Invariance Principle

The invariance principle has been applied to the automatic control field since the 1960s, and it is
well known that the feedback can reduce the effects of disturbance, but it cannot completely
eliminate its influence. Therefore, the system adopts the invariance principle so that it can
respond sensitively to disturbances.

In the open loop system of Fig. 7.13A, output C is only required to be the result of reference
input, but the pure output is:
C ¼ C R + C V ¼ GR V (7.65)

where V is the disturbance.

In Fig. 7.13B, the feedback is introduced, and the disturbance in the system output affects the
C V as follows:

V
C V ¼ (7.66)
1+ GH
In Fig. 7.13C, the disturbance is obviously smaller than that given by Eq. (7.65).

(A) (B) (C)
Fig. 7.13
Control modes of different systems.
(A) Open loop system; (B) Feedback system; (C) Invariance system.