Villamos autók szabályozott töltése az elosztóhálózaton okozott problémák elkerülésére

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Supervisor:
Dr. Farkas Csaba
Department of Electric Power Engineering

Electric Vehicles (EVs) showed environmental and efficiency advantages compared with gasoline vehicles. The number of EVs is expected to increase crucially in all over the world. Several countries already initiated governmental programs to increase EVs market share. Also, many car manufacturers produced various types of EVs which have different specifications and prices which gives the buyer a lot of options to choose from. These EVs can be charged from large charging stations, street chargers, workplace chargers and private home chargers which will be supplied from the distribution network. It is expected that this new load will have negative effects on the distribution network, so utility companies should execute comprehensive studies to understand the possible effects of this new load on the distribution network and take this into consideration in the design, operation, and planning processes. Also, techniques to minimize and alleviate these negative effects should be developed.

The thesis begins with a general background of EVs, EVs market, EVs types, and technology of batteries used in EVs. Furthermore, it introduces the benefits and challenges of EVs, EV charging technology and the environmental, economic and grid impacts of EVs.

The second part of the thesis presents a study of the uncontrolled EVs charging impacts on a real residential low voltage (LV) distribution network for different penetration levels (e.g., 12.5%, 25%, and 50%). Delayed charging was proposed to alleviate these impacts. DIgSILENT Power Factory simulation software was used to perform the study. 24-hour time series simulations were executed with a load flow every 15 minutes. The effects on the transformer loading, cables loading, voltage profile at the furthest point from the transformer, and daily energy losses were evaluated. The results demonstrated that the delayed charging had lower impacts on the LV distribution network compared with uncontrolled charging. The transformer exceeded its maximum rating for a short duration in case of uncontrolled charging and did not for delayed charging. Delayed charging may result in generating a second peak at the off-peak hours. Cable loading was very small in both charging scenarios, and the loading was higher in uncontrolled charging than delayed charging. The furthest point voltage at both charging scenarios was within the acceptable limits and lower voltage values were recorded for uncontrolled charging than delayed charging. The system was more efficient and had lower energy losses during the day in delayed charging compared with uncontrolled charging.

The third part of the thesis presents a method for controlling EVs charging. Two designs of the fuzzy logic controller were executed for management of EVs charging. The first EV charging controller depends on local inputs. As a result, no communication infrastructure is needed. The controller inputs are voltage at the point of connection and EV battery state of charge (SoC) and the output is the charging power. The second EV charging controller needs a basic communication to receive the electricity price from the electric utility which is the first input to the controller. The second input is EV battery SoC. The controller output is the charging power. The results demonstrated that the proposed controlled charging method reduced the impacts of EVs charging on the distribution network compared with uncontrolled charging.

The fourth part of the thesis presents a study of the uncontrolled EVs charging impacts on a commercial LV distribution network for 50% penetration level. Decentralize photovoltaic (PV) generation was proposed for alleviation of the negative impacts. The results demonstrated that decentralized PV generation can alleviate the impacts of EV charging on commercial LV distribution network. PV generation restored the normal operating condition of the transformer which was overloaded due to EVs charging. The cable was lightly loaded when PV generation was available compared with the case which EVs are charging and no PV generation. Better voltage profile during the day was recorded when PV generation was connected to the LV distribution network. The daily energy loss in the LV distribution network was significantly reduced by the use of PV generation.

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