The impact of EV nonlinear loads on a low-voltage grid: A case study

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Journal Title

Journal ISSN

Volume Title

Sähkötekniikan korkeakoulu | Master's thesis

Date

2022-05-16

Department

Major/Subject

Electrical Power and Energy Engineering

Mcode

ELEC3024

Degree programme

AEE - Master’s Programme in Automation and Electrical Engineering (TS2013)

Language

en

Pages

79+7

Series

Abstract

The Paris Agreement sets the foundation for reducing global emissions, and Norway contributes to this by utilizing its renewable hydropower and by having the largest Electric Vehicle (EV) market share sales in the world. The condition of the distribution grid must be evaluated with the adoption of the EVs leading to effects on Power Quality (PQ) events, a relatively unknown field of interest for distribution grid companies. Furthermore, the foundation for relying on previous research is rather weak, as it uses simplified grids in its simulations. Thus, the purpose of this study is to identify the order of PQ events that may arise by implementing EVs in a general, anonymous, and real-life low-voltage network, provided by the distribution grid company Elinett in Norway. PQ events were evaluated against their regulation thresholds for voltage drop, asymmetry, and Total Harmonic Distortion (THD), in addition to the capacity of the transformer. The Simulation tool DIgSILENT PowerFactory was used to step-wise implement EV loads in the network holding 8 customers and 18 busbars. The simulations were based on a worst-case scenario with a base-load operating at a high-load and without a diversity factor, as the penetration rates (PR) can indicate the same scenario as the diversity factor. The research found the following order of events. First, the transformer needs to be replaced due to an early-stage overload. Second, the asymmetries allowed a maximum of half the customers to have 16A and 32A chargers. Third, the THD accepted a 25\% higher PR increase for the 16A current, and the voltage drop another 25\% increase for both charging currents. The results also demonstrated that the grid is light-to-medium rigid and the presented load pattern showed a high dependency on electric heating among Norwegian homes. Furthermore, Elinett uses a set inclusion criteria strategy basing the charger size on the minimum short circuit current at the customer. The implementation of this strategy resulted in busbars E and F exceeding the limit for asymmetry, again emphasizing the importance of awareness. The remaining busbars held a decent buffer towards the thresholds as the strategy was concluded to be safe and prudent. Elinett can therefore focus less on the THD and the voltage drop, and more on the awareness of asymmetry and substation monitoring when planning projects.

Description

Supervisor

Lehtonen, Matti

Thesis advisor

Eriksen, Pål Egil
Abdelfattah, Mohamed

Keywords

electric vehicle charging, EV, charging, LV-grid, power quality

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Citation