Analysis of the maximum available time to switch the operation control mode of a distributed generation during an islanding occurrence

The operation of distributed generation systems (DG) is subjected to events such as unintentional islanding occurrences. To prevent the activation of the DG´s protections and power supply interruption, when an islanding occurs, the DG must change from grid-connected operation mode to isolated operation mode and keep the voltage and the frequency within acceptable operational levels. The available time to switch the operation control mode should be investigated to avoid false islanding detections and to minimize the negative impact on the quality of the generated energy. This paper analyzes the maximum time for switching the operation control mode of the DG, after an unintentional islanding occurrence. Simulations were carried out on the PSCAD/EMTDC. The simulated DG system is based on a diesel generator and distinct loads. Using a classical control strategy (CCS) and a fuzzy control strategy (FCS) for voltage, frequency, active and reactive powers, the maximum available switching time is analyzed. The FCS provided longer available times than a strategy using classical controllers.