Anti-islanding protection for distributed generation systems based on reactive power drift

This paper demonstrates that the close-loop control of distributed generation systems' output power has negative impacts on island detecting schemes using phase-shift techniques, such as active frequency drift (AFD), slide-mode frequency shift (SMS), etc. On that basis, an anti-islanding protection scheme is proposed, which takes system frequency as feedback to adjust the reactive power output of grid-connected inverter. This control scheme can yield a quick frequency shift in an islanding situation and trigger the detection module. Comparing with AFD and SMS, this scheme produces no current waveform distortion, and has a better performance in real power control during transient state after islanding. Corresponding mathematical model is presented. Comparison results with AFD and SMS shows the advantages of proposed anti-islanding protection scheme. Finally, simulation results validate the proposed control scheme.