Electric Vehicle Charging Integration in Buildings: Local Charging Coordination and DC Grids

Name: Juan Van Roy

Prof. dr. ir. Johan Driesen

Electric vehicle (EV) charging in buildings has a non-negligible impact on the in-building and low-voltage (LV) distribution grid. It is widely accepted that the coordination of EV charging may reduce this grid impact, allowing more EVs to be charged through the power system, without grid infrastructure investments. The literature mainly focuses on (large-scale) optimization coordination for a certain objective (technical and/or economical), which requires a relative high penetration rate of EVs to be beneficial. However, local clustering of EVs in buildings or LV distribution grids might already occur in the nearfuture, requiring local charging solutions. Therefore, in order to reduce this EV charging grid impact, this dissertation focuses on the following local EV charging solutions: (a) local EV charging strategies (rule-based control) in large buildings (multiple EVs charging), which require minimal local or EV internal knowledge, and minimal or no communication in and outside the building, and (b) the use of DC grids to connect and charge the EVs in buildings.

The objective is to assess how these solutions can already limit the grid impact, in order to allow a higher penetration rate of EVs and others, such as a heat pumps and PV systems, in the system. The following local EV charging strategies have been assessed: (a) EV based peak shaving, which reduces the EV charging power in order to maximally use the available charging time, i.e. load shifting and load reduction, (b) delayed charging delays the charging as long as possible, (c) renewable self-consumption, i.e. matching local electricity demand and production, (d) a voltage droop mechanism adapts the EV charging power as a function of the grid voltage, and (e) a building peak shaving mechanism reduces the EV charging power as a function of the total building load.

All local EV charging strategies succeed in their objectives, i.e. reducing the demand and/or injection peak powers, increasing the local self-consumption, and/or reducing the voltage deviations. The results show that these local EV charging strategies, which do not require any optimizations and any communication outside the building, decrease the grid impact and allow to charge more EVs in the building, postponing or avoiding the needs to invest in grid infrastructure reinforcements.

The use of DC grids also reduces the grid impact of EV charging in buildings. The results show that DC grids are primarily interesting regarding the voltage unbalance and voltage deviations in the AC grid. Both the voltage unbalance and voltage deviations are reduced. For the coordination strategies, which anticipate on the local self-consumption maximization, DC grids are a good solution to reduce the energy exchange with the LV distribution grid to which the building is connected.

In order to assess the grid impact of EV charging, two simulation tools have been developed: (a) the mobility behavior simulation tool, that creates realistic driving profiles for individual vehicles in the fleet, based on available statistical data for mobility behavior in Flanders, and (b) a Modelica library for electrical modeling, which can be used for the integration of different multidisciplinary energy systems in buildings and districts.

https://lirias.kuleuven.be/handle/123456789/485712

•   Prof. dr. ir. Johan Driesen (promotor)
•   Prof. dr. ir. Hugo Hens (voorzitter/chairman)
•   Prof. dr. ir. Dirk Saelens (secretaris/secretary)
•   Prof. dr. ir. Geert Deconinck
•   Prof. dr. ir. Lieve Helsen
•   De heer Gerrit Jan Schaeffer
•   Dr. Andrew Keane , University College Dublin