Voltage unbalance in low voltage networks with single-phase and three-phase micro-generation and loads

Abstract

The incorporation of clean energy sources in the power system is a topic of discussion almost everywhere. After the "wind (farms) of change", small, dispersed, urban photovoltaic (PV) generators are being installed in the roofs of the buildings, connected to the local Low Voltage (LV) grid. A boost in this type of renewable micro generation is expected in the near future. Due to the domestic loads, LV grids are inherently unbalanced, its analysis requiring the use of three-phase load flow methods. This same methodology is used in this paper to assess the problem of the concurrent unbalanced generation and load and to cope with the presence of both single and three-phase equipment in the same grid. A review of existent models for three-phase equipment is performed. The issue of modelling three-phase loads (isolated star and delta connected) and singlephase PV generators and associated power electronics is given special attention. Finally, a case-study is presented, enabling to draw some conclusions regarding the impacts on the Medium Voltage (MV) grid and the behaviour of the system facing different climacteric conditions.