Islanding phenomenon of a grid-connected independent generator like a photovoltaic (PV) system occurs when a section of a utility system is disconnected from the main utility voltage source, but the independent generator continues to energize the utility lines in the isolated section. Since islanding causes a safety hazard to utility service personnel and damage to power supply facilities as a result of unsynchronized reclosure, PV inverter is required to have anti-islanding function. In order to prevent this phenomenon, various anti-islanding methods have been studied. Even though phase shift anti-islanding method including slip mode frequency shift (SMS) method and reactive power variation (RPV) method has been regarded as a highly effective anti-islanding method, the analytical design method of that has not been cleared. This paper proposes a design guideline of the phase shift anti-islanding method based on non-detection zone (NDZ). As leading phase shift anti-islanding methods, both SMS and RPV methods are discussed to verify the validity of the proposed method. Both methods are derived analytically through the modeling and verified visually by simulation and experiment under IEEE Std. 929-2000 test condition. It is shown that both methods designed by the proposed method have effectiveness to detect islanding within 2 s and good power quality above 0.99 power factor. The presented methodology in this paper can be extended to design other active anti-islanding methods. (C) 2007 Elsevier Ltd. All rights reserved.