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The proliferation of Electric Vehicles (EVs) poses new challenges for the Distribution System Operator (DSO). For example, the rectifiers that are used for charging EV batteries could significantly influence Power Quality (PQ), in terms of harmonic distortion. The emissions from individual EV, are well regulated by current harmonic emission standards. But what the aggregation of multiple EV loads will look like is still uncertain and the research being made in this area is still in its early stage. 

The DSO responsibilities include ensuring grid code compliance confirmed by PQ metering.  In general, 10 minute RMS values are sufficient. However, the large scale integration of non-linear loads, like EVs, could lead to new dynamic phenomena, possibly lost in the process of time aggregation.

In this thesis PQ and, in more detail, the concept of harmonics, and how this is related to EVs, is presented. A current-harmonic load model using power exponential functions and built from actual measurement data during the individual charging of four different fully electric vehicles was constructed. The model was based on individual emitted current harmonics as a function of state of charge (SOC), and was used to deterministically simulate the simultaneous charging of six vehicles fed from the same bus. The aggregation of current harmonics up to the 11th was simulated while randomizing battery SOC, the start of charging, and the kind of vehicle. Additionally, an investigation of the impact on aggregation in time was conducted.

The analysis clearly shows the importance of phase angle information, its correlation to SOC, and how the aggregation of EV loads is influenced by these factors. The analysis also shows that 10 minute RMS aggregation could lead to significant deviations from the “actual” (200ms) data.  This indicates that 10 minute value monitoring could lead to information losses.

This paper presents an aggregate current-harmonic load model using power exponential functions and built from actual measurement data during the individual charging of four dierent fully electric vehicles. The model is based on individual emitted current harmonics as a function of state of charge (SOC), and was used to deterministically simulate the simultaneous charging of six vehicles fed from the same bus. The aggregation of current harmonics up to the 11th was simulated in order to find the circumstances when maximal current-harmonic magnitude occurs, and the phase-angle location. The number of possible identical vehicles was set to four, while battery SOC, the start of charging, and the kind of vehicle were randomized. The results are presented in tables, graphs, and polar plots. Even though simulations did not consider the surrounding harmonics, supply-voltage variation, or network impedance, this paper presents an innovative modeling approach that gives valuable information on the individual current-harmonic contribution of aggregated electric-vehicle loads. With the future implementation of vehicle-to-grid technology, this way of modeling presents new opportunities to predict the harmonic outcome of multiple electric vehicles charging. 

Conservation voltage reduction (CVR) is based onthe premise that conserving energy by reducing voltage levels of the electrical system will lead to reduced electrical energy consumption. In this work a comparison-based method has been applied for assessing CVR effects in a distribution grid. The reference voltage on the secondary side of the primary substation was manually altered according to a predefined schedule during 6 months, that is, perform CVR on a substation and apply “normal” voltage to the same substation with a 2-week interval between the changes. Measurements (1 second RMS-values for voltages, active powers and reactive powers) and analysis were made at the 11 kV side of a 130/11 kV transformer of a primary substation, on outgoing feeders and at the 400 V side of 11/0.4 kV distribution transformers downstream of the primary substation as well as on downstream single rural and industrial customers. Active power at different reference voltage levels versus 24 hours divided into 10 minute intervals for reoccurring days of the week were plotted and analysed.

This work confirms the difficulties in obtaining predictable loads over time and to accurately analyse the load composition on all grid levels. Each are needed in order to quantify the effects of CVR and by extension optimising the grid operations without violating the power quality.

Electric vehicles (EVs) poses new challenges for the Distribution System Operator (DSO). For example, EVs uses power electronic-based rectifiers for charging their batteries, an operation that could significantly impact Power Quality (PQ) in terms of harmonic distortion. The DSO responsibilities include ensuring grid code compliance confirmed by PQ metering. In general, 10 min rms values are sufficient. However, the large scale integration of non-linear loads, like EVs, could lead to new dynamic phenomena, possibly lost in the process of time aggregation.This paper presents an analysis of the impact on time aggregation (3 s-, 1min-and 10 min rms), when modelling current harmonics of aggregated EV loads, using power exponential functions. The results indicate that, while3 s rms and 1 min rms marginally affect the outcome, 10 min rms aggregation will lead to a significant deviation (>30%) in terms of maximum current harmonic magnitude.