Page 235 - Mathematical Models and Algorithms for Power System Optimization

Optimization Method for Load Frequency Feed Forward Control 227

Therefore, the mathematical model of each block except the excitation is considered, and the
equivalent model of the power system is established.

This chapter uses decomposition techniques to decompose a complex system into easily
solvable subsystems and to handle the consistency between the solution of the subsystem and
the solution of the system.
On the basis of the establishment of the mathematical model and the power system equivalent
model of each block of the power plant, according to the situation where the lowest level of the
power system is the power station or generator set, and the second level is the dispatching
center at all levels, state estimators of all levels are hierarchically constructed by the
hierarchically decomposed ideas.

In summary, the state estimation of the hierarchically structured power system should use the
hierarchical estimation method. Two-stage estimators have been applied to the power system,
that is, local estimator and central estimator. Because variable Δω j in the system can be
measured only by the cheap frequency meter, Δω j is taken as a measured variable. Based upon
the power system model, all state variables of the system can be estimated using the Kalman
filter, so as to estimate the system operation status (frequency changes) and predict the
changing trend of load disturbance.

7.2.3 Way of Setting Up the Load Frequency Controller based on the Invariance Principle

The task of the load frequency controller is to find a control law to compensate for the influence
of the load disturbance to maintain the power system frequency within the allowable range of
the specified value. The integral feedback controller can attenuate the effect of the disturbance,
but it cannot completely cancel it out. However, under certain conditions, the feedforward
controller (or compensator) based on the invariance principle does not suffer from the effects of
disturbances. That is, a control law can be found to completely compensate for the disturbance
and control the frequency change.
The power system load frequency controller has an integral type and a state feedback type. This
chapter attempts to apply the invariable principle to establish a new type of discrete
compensation controller suitable for digital control to compensate for the load disturbance of
the system so as to control the system state.

In the past, the feedback control did not need to resist the system disturbance,
that is, without any compensation to the disturbance, and the control was left after the
state of the system was changed. In general, the feedforward control is to perform
compensation control after disturbance measurement. If the system can be continuously
measured, estimated, forecasted, and controlled, the tracking control to the power
system can be achieved.