Case Study of Photovoltaics and Electric Vehicle Charging in a Low-Voltage Distribution Grid

Abstract: This thesis investigates the effects from a grid connection of photovoltaics and electric vehicle charging in a low-voltage distribution grid. The study has taken place on behalf of Norrtälje Energi AB, and the object of study is a customer in one of their rural grids. Due to reported disturbances by the customer, a Magtech Voltage Booster (MVB) was installed at the point of common coupling. To evaluate the situation, three power quality measurements were analysed. Furthermore, a model of the distribution grid was developed in OpenDSS. The main conclusion of this thesis is that the disturbances seems to be caused by temporary voltage drops (below 195.5 V) during charging hours. This situation continues to create problems even though the MVB boosts and balances the voltage. The power quality measurements showed that the voltage unbalance, during charging hours, violated the limit both before and after the MVB-installation. Another significant conclusion in this thesis is that the MVB does not seem to improve the power quality, on the contrary it deteriorates the power quality with regards to rapid voltage change and harmonic content. Furthermore, the OpenDSS-model was able to predict the temporary voltage drops. And the model also resulted in voltage unbalance comparable to the measurements. The model also displayed how the voltage unbalance and harmonic content mitigated to other parts of the grid, and it became clear that it is only the closest neighbour that is in the risk of deteriorated power quality.