Abstract:
A large-scale power system is composed of multiple control areas that are connected
to each other through tie lines. As active power changes, the frequencies of the areas
and tie-line power exchange deviate from their scheduled values which may greatly
degrade the performance of the power system.
Load frequency control (LFC) has two major assignments, which are to maintain the
standard value of frequency and to keep the tie-line power exchange under schedule
in the presence of any load change. An area control error (ACE), defined as a linear
combination of tie-line power and frequency deviations, is regarded as the controlled
output of LFC. LFC regulates ACE to zero. When dealing with the LFC problem of
power systems, unexpected external disturbances, parameter uncertainties and model
uncertainties of the power system pose big challenges for controller design.
Active disturbance rejection control (ADRC) generalizes the discrepancy between the
mathematical model and the real system as a disturbance, and rejects the disturbance
actively, hence the name active disturbance rejection control. As a result controller
does not require accurate model information and is inherently robust against
structural uncertainties.
In a power system, synchronous machine electrically closer to the point of impact
picks up the greater share of the load regardless of their size. Moreover, generators
nearer to the disturbance show largest response and rest of the generators show
smaller response. The inertia constant (H) of generators affects the system frequency
response. It has been observed that the minimum frequency deviations belong to the
generators that have larger inertia constant and response of generators with lower
inertia constant responses faster during the disturbance of an interconnected system.
Tie-line power exchanges between two areas depend on the tie-line synchronizing coefficient
and the frequency of two areas.
An LFC controller that incorporates these factors in its design is expect to show faster
and better response characteristics.
