Frequency control enhancement of an islanded microgrid using disturbance-observer-based approach

ABSTRACT

Load frequency control (LFC) is a major challenge for a microgrid (MG) system due to complex, nonlinear and uncertain behaviour of distributed energy resources (DERs) and fluctuating power demand. This study presents disturbance-observer-based control (DOBC) as a part of secondary control scheme in the frequency stabilisation of an islanded multi-source MG system. A dynamic frequency response model of MG system is considered with a variety of DERs, including renewable and reserve energy sources. An unscented Kalman filter (UKF) is proposed as an estimator to observe the disturbance augmented as one of the states, practically corrupted or inaccessible.Subsequently, a DOBC strategy is designed and implemented to stabilise the frequency considering unfavourable effects derived from the uncertainties, disturbances, transients and measurement noise. The benchmark MG model and control methodology are developed using MATLAB environment. Further, the robustness of the present DOBC scheme is investigated subject to the random and non-random disturbances. The simulation study demonstrates the efficacy of DOBC approach, and then a comparative analysis validates the contribution of disturbance-observer-based load frequency control (DOBLFC) approach in enhancing the secondary control performance to better restrain the frequency deviation over the conventional control.

KEYWORDS:

• Microgrid
• island mode
• load frequency control
• disturbance observer-based controller
• robust estimation