Abstract

The frequency stability is a basic principle in the micro-grid (MG) system operation. Various reasons such as, the reduction in system inertia due to the replacement of traditional generating units with a large amount of renewable energy sources (RESs) cause undesirable influence to MG frequency stability, leading to weakening of the MG. Furthermore, sudden load shedding, load restoring, and short circuits cause large frequency fluctuations which threaten the system security and could lead to complete blackouts as well as damages to the system equipment. Hence, this paper proposes a coordination of Load Frequency Control (LFC) and digital under/over frequency relay for a small MG protection considering different cases study of load change and high integration of photovoltaic (PV) and wind farm. The discrete-time data of system frequency which obtained from data conversion system is applied for energizing the digital frequency relay under the normal and faulted conditions. The proposed digital frequency relay will include both over and under frequency functions. To prove the efficient effect of the proposed coordination, the MG was investigated for the MATLAB/ Simulation. The obtained simulation results stated the effectiveness of the proposed coordination to maintain the power system frequency stability and security. Furthermore, the superiority of the under/over digital frequency relay in terms of accuracy and speed has been approved.