Temporal analysis of power system violations due to electric vehicles: The case of the Swedish low-voltage distribution grid

Abstract

Vehicle fleet electrification is part of the strategy to meet the European Green Deal targets. Thus, while electric vehicles (EV) are becoming increasingly popular among Europeans, implications of an escalated charging demand for the electricity grid are yet to be explored. Since electricity demand follows temporal patterns throughout the year, the time dimension of impacts takes on great importance. This thesis analyses the implications for the low-voltage (LV) electricity distribution grid from a high EV penetration scenario, considering Sweden and the year 2050 as base assumptions. Current regulations on thermal and voltage violations in feeder cables and transformers are used to assess the impact on the grid. Two models are employed to simulate the scenario: (i) a cost optimization model to predict the future energy system structure and electricity dispatch; (ii) a reference network model to simulate the Swedish LV distribution grid capacity and operation. Furthermore, grid vulnerability findings are leveraged to provide feedback to the energy system model. Hence, presenting a flexible future energy system that will allow the application of smart charging strategies to preserve electricity network components. The results show that frequent power system violations would be registered, especially in winter months and the evenings when residential electricity demand in Sweden is elevated. Yet, price-optimization charging strategies mitigate this correlation and breaches of grid regulations are significantly reduced. Vehicle-to-grid (V2G) charging is also examined, presenting no advantages compared to a unidirectional flow price-optimization approach in terms of grid susceptibility. Furthermore, findings show that many violations occur when EVs charge at maximum charging power rate (CPR) at certain time intervals of the day. Hence, as a grid vulnerability alleviation solution a temporal CPR constraint is suggested, leading to a notable reduction of grid issues. In terms of electricity production mix, a system mainly composed of wind power and hydropower with a few backup technologies provides flexibility to securely accommodate EVs in the LV distribution grid.