A Hybrid Islanding Detection Method Based on the Rates of Changes in Voltage and Active Power for the Multi-Inverter Systems

Abstract

This paper proposes hybrid islanding detection for inverter-based distributed generation (DG) units. Conventionally, passive islanding detection methods may fail when power mismatches are nearly zero. Also, the difficulty of setting threshold is another common problem. To overcome this drawback, a new procedure for islanding detection is proposed based on the combination of the rate of change of voltage (ROCOV) and the rate of change of active power (ROCOAP). The ROCOAP is only activated when the islanding condition is suspected by ROCOV. When the power mismatch is negligible, some high-impedance fault or non-islanding events occur, the proposed method can identify islanding, thus presenting a combination of advantages of each passive/active method. Therefore, it is useful to appropriately detect islanding situation in all-inclusive of scenarios. Consequently, the proposed method under several conditions, such as pulsating loads, pre-energized transformers have been considered. To illustrate the effectiveness of the proposed approach, various tests such as UL1741 have been investigated. Comparison analysis shows that the suggested method is more acceptable and the NDZ is reduced significantly. In addition, proper performance even for small power mismatch is illustrated by presence of variety of non-islanding events and improvement of power quality is achieved in comparison active method.