Anti-islanding Detection Method using Phase Shifted Feed-Forward Voltage

A grid-connected inverter should stop supplying energy to the local load when the grid is disconnected. It is called anti-islanding. To detect the islanding operation of inverter, many islanding detection methods were generally employed. Anti-islanding methods are divided into two groups: active methods and passive methods. Active methods generate the perturbation to change grid parameters such as magnitude of grid voltage and frequency in the allowable range. Most active methods using frequency variation generate the reactive power in accordance with the grid frequency. In this paper, a new islanding detection method is proposed. The proposed method uses the feed-forward voltage of the current control loop to make positive feedback on frequency. The phase angle of feed-forward voltage shifts according to the grid frequency variation. Thus, in the islanding condition, phase shifted feed-forward voltage makes inverter output voltage leading or lagging. Through the principle, the proposed method generates reactive current and drifts grid frequency out of the allowable range in the case of islanding operation. The feasibility of the proposed method was verified by computer simulations and experiments based on 600W inverter system.