Performance of the OVP/UVP and OFP/UFP Method With Voltage and Frequency Dependent Loads

In previous literature, constant RLC loads were assumed to impose, on the islanding detection method, the hardest detectable case. For this reason, distributed-generation (DG) islanding studies are usually analyzed and performed by using constant RLC loads. In this paper, different types of loads are taken into account by modeling the load´s voltage and frequency dependence. The performance of the over/undervoltage and over/underfrequency protection (OVP/UVP and OFP/UFP) method is examined for the different load models and the results are compared with the constant RLC load case. The analysis is conducted on a constant power-controlled DG designed to operate at unity power factor. A generalized formula, for calculating the nondetection zone of the OVP/UVP and OFP/UFP method, is derived in terms of the load´s voltage and frequency dependence parameters. The analysis is further extended on a constant current-controlled DG interface.