Due to environmental concerns related to climate change, fiscal incentives from governments around the world, and falling prices of proved and ever-improving technology, the use of renewable energy sources has been rising considerably over the past years. A considerable amount of these sources, among which solar is to be highlighted, is used by gridconnected generators that are installed in electrical distribution systems. Solar photovoltaic generators are characterised for using an intermittent source of energy. Since they do not have any moving parts and therefore no inertia, variations in irradiance levels directly and instantaneously affect output power. Therefore, fluctuations in generated power from PV systems result in unbalancing between consumption and generation. In such context, this project aims to study the impact of high PV systems penetration in voltage and unbalance levels of electrical distribution feeders, such as percentages of unbalance and rise in pu voltage that can be expected under a certain penetration level of distributed PV generation, feeder sensitivity to photovoltaic penetration, times of the day when maximum unbalance can be expected… among others. After a literature review that defines power quality issues and the power-flow analysis method, the methodology for the analysis is presented. Two software tools, OpenDSS and MATLAB, have been integrated to program the code that is necessary to run the simulations that will provide the necessary results. The general characteristics of the resulting code are reviewed. Three types of analysis have been implemented: 1. Snapshot analyses, which provide the state of the system under certain loading conditions; 2. Feeder sensitivity to PV penetration analyses, which calculate the highest unbalance that occurs in the feeder under increasing PV penetration conditions; and 3. Time-series simulations, which use time-series solar irradiance and load data drawn from real sources to simulate realistic situations. These analyses have been performed on two very different feeders: on a smaller, 37-Bus delta-connected distribution feeder from IEEE, and on a bigger, 2998-Bus wye-connected distribution feeder from EPRI. The results of these simulations and the conclusions regarding the main objectives are then presented. Outgoing