Analysis of fast acting active disturbance rejection control based load frequency control

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.