ENS detection algorithm and its implementation for PV inverters

Because of the increased use of photovoltaic (PV) installations, new and more stringent power quality requirements are being issued. Continuous grid monitoring is always a matter to be considered in order to detect islanding operation. One of the severe standards in this field is the German ENS standard. An overview of the methods used for online grid measurement is given and emphasis is put on one new method based on the injection of a non-characteristic harmonic in the grid. The algorithm for ENS detection used by the PV inverter when running on both pure resistive and highly inductive networks is described in detail. Laboratory results obtained from the tests carried out on an existing PV inverter are also presented and show that the method works very well.