Islanding detection and control in wind-solar hybrid distributed generations

Abstract

As electricity demand surges in most developing countries, there is a need to tap into other sources of energy. Renewable energy sources are mostly preferred due to their reduced environmental pollution compared to other sources. However, integrating the renewable sources is challenged by islanding: one of the serious issues with distributed generation (DG) integrations. Islanding occurs when a DG becomes electrically isolated from the main grid but continues to power the local loads or a portion of the power system. Voltages, frequencies, third harmonic distortions, and currents are always outside of specified limits in such situations. This poses a significant risk to utility workers as well as local loads. This project examines various anti-islanding (AI) protection relays when the islanding condition of a grid-tied wind-solar hybrid system appears at the Point of Common Coupling (PCC) between the hybrid Power System and the power grid. 150 kW wind-solar hybrid distributed generation was designed and modelled in Simulink for study. Various grid fault scenarios were also simulated, and the results compared to islanding conditions. The simulation graphs and detection times during grid faults and islanding conditions are recorded in this paper. The results show that, the passive detection techniques, mainly over/under currents, and voltages as well as rate of change of frequency, could detect islanding condition in about 0.104 seconds. Upon several iterations and series of simulations, the results were found to fall within the acceptable limits provided by IEEE Std.1547-2003 of under 2 seconds. For a single-phase-ground, phase-phase, and phase-phase-ground grid faults, the detection technique detects islanding but fails to trip the circuit breaker. The inability of the detection techniques to trip the circuit breakers under grid fault conditions is desirable to avoid false tripping. Various explanations and recommendations are provided in the results section.