Assessment of electric cars’ charging impact on the low-voltage distribution network

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Dr. Farkas Csaba
Department of Electric Power Engineering

The goal for this thesis is to investigate the effect of a new type of technology that has been thriving in the last ten years in term of usage. The share of energy generation from solar power reached a level never seen before as more and more people are trying to decrease their electricity bill. Furthermore, due to increasing fuel costs and the increase of environmental awareness, electric car sales are in the rise with the expectation that more and more vehicles, for example, trucks, will use the technology of electric motors with or instead of internal combustion engines.

Both of the aforementioned technologies make use of power electronic devices. These devices are well known for their not so good effect on the system although they serve the purpose of supplying power, converting from alternating to direct and vice versa. By doing so they inject harmonics to the system.

Solar generation is controlled by the amount of solar radiation delivered to the surface of the cell during the day, which is far from constant hence creating the problem of voltage fluctuation.

Electric car charges will contribute to this problem as the owners control the charging behavior, which is most of the time done in the night hours creating a new peak demand and voltage drop. Both harmonics and voltage fluctuation are considered as power quality problems that will affect the low voltage distribution network, which is the main concern in this thesis.

To assess the impact of electric car charging systems and solar generation, computer simulations were done. A real-life grid was used with real-life loads, with and without the single chargers and photovoltaic systems to be able to compare the results. DIgSILENT Power Factory was used to perform the simulations and obtain the results. We also used Python programming language to automate the simulation procedure and also to conduct stochastic load-flow simulations, i.e. run a number of simulations with different data sets according to distributions determined based on literature review.

Penetration of new loads with power electronic devices (nonlinear devices) are part of the problem of power quality as these loads increase the harmonic content in the network, hence more increased consequences will be manifested in higher voltage drops, voltage fluctuation, current distortion.

The voltage drop occurs when a large number of electric cars are charged at the same time which may simulate a real-life event, so distributing charging time may solve the problem.

Higher penetration of photovoltaic generation systems was simulated according to real life generation data, hence an overvoltage across the feeders, especially during the midday when the power production of the photovoltaic system is the highest will change the direction of the power flow, hence the voltage drop will occur towards the upstream power flow.


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