Network planning for charging electric vehicles in Stockholm

Abstract: This master thesis project analyses how an increased number of electric vehicles would affect the electric network in Stockholm. The project was started in order to help Ellevio, the DSO of Stockholm, understand how to manage the increased amount of requests of network-capacity connected to electric vehicle charging. Five different areas have been simulated in the software Tekla to investigate how many electric vehicle chargers with a rated power of 3.7 kW that can be run at the same time without exceeding network limits in terms of voltage drops in consumption points, maximum current in cables and apparent power in the secondary substation. Two different charging curves spanning over eight hours each were used during the simulations to achieve the worst plausible scenario. The first charging curve took place between 16:00-00:00 and the second between 22:00-06:00. By using two charging curves it was possible to investigate if more electric vehicle charging could occur at the same time if the charging is moved to night time. The results show that the first problem to occur in all investigated areas is overloads of cables. However, this problem can be remedied in especially areas with apartments and in the city by using equipment which can reduce the output of the chargers depending on the load magnitude of the line connection. The city network could handle highest numbers of charging without exceeding the limits, followed by the areas with apartments and at last the areas with small houses. However, it can be seen in the results that the small house areas can handle about the same number of chargers as the city network if a few cables are replaced. Finally, all areas can handle more charging without exceeding the limits if the charging is moved to night-time.