Phasor measurement units performance in three-phase unbalanced systems

Phasor Measurement Units (PMUs) are the most modern measurement devices for electric power networks. Their performance, in terms of synchrophasor, frequency and rate of change of frequency (ROCOF) measurement accuracy are crucial for the overall performance of the network management and control applications that are expected to rely on PMU-based distributed measurement systems. In this regard, PMU performance should be assessed under different conditions. IEEE standard C37.118.1, which is particularly focused on PMUs for power transmission systems, reports tests and requirements for PMU compliance. However, some important operating conditions are neglected. In particular, the presence of unbalance in the three-phase system appears relevant for an advisable application of PMUs to distribution networks. In this paper, the impact of unbalance on two important classes of PMU algorithms is discussed. Analytical formulas are derived to estimate the effect of unbalance on synchrophasor, frequency and ROCOF estimations, and they are verified by means of numerical simulations.