An Improved Active Frequency Drift Method for Anti-Islanding Based on Correlation Technique

Abstract

In order to prevent islanding, many anti-islanding methods have been researched since 1980. One of the most known anti-islanding methods is an active frequency drift (AFD) method. This AFD method makes the PV inverter operating frequency to be reached out over frequency or under frequency relay. By depending on the frequency relays to determine islanding, it takes more time to detect islanding and also it can generate large harmonic components for antiislanding. In response to this concern, this paper presents an improved active frequency drift method for anti-islanding by using correlation technique. Without depending on the frequency relays, the proposed method uses a calculated correlation factor to determine islanding. The proposed method uses the characteristics of which the distorted current by AFD method had a strong correlation with the frequency of PV output voltage when islanding occurred. On the other hand, when the grid is connected, the PV inverter voltage is dominated by the rigid grid voltage source and it had a week correlation with the distorted current by AFD method. As a result, the proposed method has high islanding detection capability and also it can detect islanding faster with higher power quality rather than depending on the frequency relays.