Voltage Ripple-Based Passive Islanding Detection Technique for Grid-Connected Photovoltaic Inverters

One of the main challenges of integrating distributed generation into the power grid is islanding, which occurs when a disconnected power line is adversely energized by a local distributed generation source. If islanding is not quickly detected, it can present serious safety and hazardous conditions. Conventional passive detection techniques used today are entirely dependent on the parameters of the power system, which under certain operating conditions may fail to detect islanding. In this paper, a novel and efficient passive islanding detection technique for grid-connected photovoltaic-based inverters is presented. In this technique, the ripple content of the inverter output voltage at the point of common coupling is monitored for deviations using time-domain spectral analysis. Islanding is then detected whenever the ripple spectral content exceeds a preset threshold level for a certain period of time. The performance of this technique was extensively tested and quantified under a wide range of operating conditions. It was determined that the proposed technique did not exhibit any non-detection zone and was able to detect all types of islanding cases within 300 ms of the allowed delay time. Furthermore, the proposed technique was found to be robust and inherently immune to other degrading factors, since it is relatively independent of system parameters, power system scaling, or the number of distributed generation sources present within the islanding zone.