It is very difficult to detect an islanding condition of a power distribution line with conventional voltage or frequency relays, while the output power and the load power of utility interactive PV inverter units are in nearly balanced state in both active power and reactive power, because a big enough voltage or frequency change can not be expected at such a balanced state.
Many studies have been reported to complement dead bands in combination of active and passive methods to prevent the islanding so far, but none of them have been succesful. This paper presents the principle of a new active method called as slip mode frequency shift (SMS). With this method the reactive power between the inverter and the load is made unbalanced intentionaly to cause the frequency to shift as if it slips down a slide. The Performance that the dead bands are eliminated effectively in the range of practical use has been examined through simulation and experiments.