Electric vehicles in the Nordic countries: Control strategies for coordinated grid services

Abstract

Nowadays, power system operators face challenges in supporting a stable and economic future power system based on renewable energy production and new types of flexible demand, such as electric vehicles (EVs). One of the main challenges is to address the adverse effects that the EVs may have on local distribution grids (distribution system operator (DSO) perspective) and enhance their usage to optimize utilization of renewables on a national/regional scale (transmission system operator (TSO) perspective). The research emphasis of this thesis is on power and energy services that EVs can provide both locally and system-wide. Three main topics are addressed: 1. Identification of current policies and barriers for system-wide and local grid service provision from EVs, as well as possible conflicts between TSO and DSO when acquiring such services. This problem comes from the TSOs’ need for grid stability services from small dispatched units, and the simultaneous interest of the DSO not to have power provision from distributed energy sources violating the local grid constraints. The acquisition of such flexibility services from one grid operator may cause undesired effects to another operator: technical and economical conflicts may arise, and a detection and categorization strategy is proposed. 2. Investigations on the suitability of standard-compliant commercial hardware (series-produced EVs and chargers) for the provision of uni- and bi-directional grid services, in order to detect the technical challenges related to EVs control for grid balancing purposes. This was the starting point for the development and implementation of standard-compliant control logics able to guarantee power system frequency stability both on a simulation and on a laboratory validation level. Possible smart EV control solutions are proposed, which aim at stabilizing frequency oscillations, at reducing reserve provision error, and at providing a trade-off between error and the overall efficiency of the fleet power converters. Further, system stability is studied both on a microgrid and on a full-scale power system level in order to outline requirements for the overall fleet output, to secure an aggregated response that does not harm the system stability 3. Identification of the technical impacts on the distribution system due to massive EV penetration levels and investigation of the effectiveness of reactive power provision from EV chargers. In general, reactive power modulation allows a reduction of the self-induced under-voltage conditions caused by EVs charging at distribution grid levels, but how effective is this solution in practice? An analytical study is conducted, which aims to assess reactive power provision from EVs in typical distribution grids. In conclusion, the research at a whole investigates the broad topic of EV integration from different stakeholders’ point of view, such as market operators, DSOs, TSOs and EV aggregators. The proposed solutions and control strategies are expected to significantly contribute to the real power system operation, in order to pave the way for a harmonic, economic and safe utilization of the increasing number of EVs.