Detection Performance and THD Analysis of Active Frequency Drift for Anti-Islanding

Abstract

:Islanding is a phenomenon that EPS(Electric Power System) is continuously energized by PV PCS(Photovoltaic Power Conditioning System) even when EPS is isolated from the grid. Unintentional islanding will result in safety hazard, power quality degradation and many other issues. So, islanding protection of grid-connected PV PCS is a key function for standards compliance. Nowadays, many anti-islanding schemes are researched. But existing anti-islanding schemes used in PV PCS have power quality degradation and non-detection zone issues. This paper analyses not only detection performance of existed anti-islanding schemes using active frequency drift but also THD of PCS output current according to each value disturbance for anti-islanding. In addition, the lowest value of disturbance in each scheme was tabulated under guarantee of anti-islanding condition.

A modified active frequency islanding detection method based on load frequency and chopping fraction changes

“…The authors in refs. [4,5] presented a method to detect islanding by monitoring a change in harmonic components of voltage. Although islanding can be identified instantly by using such a manual technique, the problem of NDZ persists.…”

“…Although islanding can be identified instantly by using such a manual technique, the problem of NDZ persists. 5,6 In general, if the power mismatch is large (ΔP > 20% or ΔQ > 5%), it is easy to detect islanding as the grid voltage and frequency are out of tolerance. On the other hand, the NDZ is undetectable by the power mismatch when the mismatch is smaller than the above-mentioned values when the load voltage or frequency stays unchanged.…”