The public defense of Georgios Foskolos’s licentiate thesis
The public defense of Georgios Foskolo’s licentiate thesis in Energy and Environmental Engineering will take place at Mälardalen University, room R3-131 (Västerås Campus) and virtually via Zoom at 9:00 on mars 5, 2021.
Title: ”Current harmonic modeling of aggregated electric vehicle loads in the low voltage grid”.
The faculty examiner is Professor Lennart Söder, KTH, The examining committee consists of Professor Professor Lennart Söder, KTH, Professor Jan Isberg, Uppsala Universitet och Dr. Valentina Zaccaria, MDH.
Reserve is Professor Lennart Harnefors, KTH.
About a quarter of all energy-related greenhouse gas emissions can be attributed to the transport sector. In order to meet the objectives of the Paris Declaration on Electromobility and Climate Change, which require at least 20% of all road transport vehicles globally to be electrically powered by 2030, the deployment of electric vehicles (EVs) is necessary.
Political frameworks and environmental awareness are both driving forces that have led to great growth in EVs, both globally and nationally. In Sweden, the annual growth since 2016 has been more than 50%. Last 12 months the growth has actually been more than 80% and at present (January 2021), there are more than 180 000 chargeable vehicles in the Swedish vehicle fleet. The forecast from Power Circle (an interest group for the electric power industry) states that this volume in 2030 will be over 2 500 000.
This development can however have negative effects on the electrical distribution network, e.g. increased peak power, and increased losses, power quality issues and overloading of transformers.
In this work, one of these potential problems has been studied - an area within power quality called harmonics. This problem is a consequence of the fact that batteries within EVs are charged with direct current (DC), provided by the rectifier, which converts alternating current (AC) to DC. During this process, the power electronic circuit of the rectifier and its control strategies will cause a distortion of the charging current which in turn may cause distortion in the supply voltage. Since different manufacturers have different rectifiers and control strategies, the harmonics will vary and therefore the combination of different EVs will vary too.
This work presents a measurement-based current harmonic model, which has been used to simulate the multiple EV charging. The model has also been used to evaluate the effects of aggregation in time, that is, what happens when the original 200 ms values are aggregated to 3s, 1 min and 10 min values.
The analysis shows how battery state-of-charge and the type of vehicle will influence the aggregation and also why phase angle measurements are important. The evaluation of aggregation in time also shows that 10 min value monitoring will result in information losses.