Page 254 - Mathematical Models and Algorithms for Power System Optimization

246 Chapter 7

dispatching center. In terms of the current situation, the estimation shall be considered only
for the first two levels.

The decomposition, multiorder, and hierarchical system theories can provide a useful
foundation for large-scale power system control. With the decomposition technology, a
complex system can be decomposed into easily solved subsystems, and the recombination of
subsystem solutions can determine the solution for the whole system. In view of the interaction
between subsystem solutions, it is often required to repeatedly deal with the relationship
consistency between the subsystem solutions and the solution of the whole system.
The reason why this decomposition method is explored in power system control is due to the
high costs to deliver messages from remote areas to the control center under any circumstances,
and the fact that collected information is used for local operation only.
The successful control of the power system depends on an accurate knowledge of its states at
any time, and some states are determined from direct observation of distributed measuring
equipment. The speed and placement of measuring equipment depends largely on the function
of the control system to the disturbance. The introduction of computer control requires reliable
data to achieve effective control. The online state estimation has provided a reliable data
foundation to the future system variables.

In conclusion, the hierarchical estimation method is employed to make state estimation to the
power system with hierarchical structure, using two-stage estimators applied to the power
system, that is, a local estimator and a central estimator. Because variable Δω j in the system can
be measured using only the cheap frequency meter, Δω j is taken as a measured variable. Based
uponthepowersystemmodel,allstatevariablesofthesystemcanbeestimatedusingtheKalman
filter. The coordinated operation of local estimator and central estimator is shown in Fig. 7.12.

Central estimator

Local estimator 1 Local estimator j

Unit 1 Unit j

Fig. 7.12
Coordinated operation of hierarchical estimator for the power system.