Voltage unbalance assessment in secondary radial distribution networks with single-phase photovoltaic systems

This research describes a way to analyze voltage unbalance sensitivity for different maximum sizes of a single-phase photovoltaic system (SPPVS) with multiple PV penetration levels in a typical secondary radial distribution network (SRDN) in Spain. This analysis effectively assesses current requirements as specified in regulations concerning maximum size to be connected. It thus helps distribution network operators to define optimal limits, depending on their context. A stochastic assessment method is proposed to account for any random combination of SPPVSs in an SRDN. In addition, this method evaluates weekly voltage unbalance during a one-year time period, on the basis of 10-min intervals. More specifically, the voltage unbalance in SRDNs with SPPVSs is assessed for each 10-min interval by means of a probabilistic radial three-phase load flow (RTPLF). The results obtained show the maximum sizes of the SPPVS to be connected as a function of the PV penetration level in the SRDN, where high PV penetrations can produce voltage unbalance problems.