Svært interessant lesning med mye referanse til Rønnberg .
The recent increase in large converter-based devices like electric vehicles and photovoltaics increases supraharmonic emissions in low-voltage grids, potentially affecting customer equipment and the grid. This paper aims to give an overview of the different factors influencing supraharmonic...
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The Propagation and Interaction of Supraharmonics from Electric Vehicle Chargers in a Low-Voltage Grid
During the measurements, another type of interaction between devices is observed in the form of “frequency beating” and intermodulation, in some cases resulting in the tripping of residual current devices. This interaction is further analyzed in order to better understand the possible impact it can have on the grid.
On the other side, the immunity of end-user equipment to supraharmonic disturbances has already been studied to some extent [
19]. Most electronic equipment uses EMC filters with capacitors to remove high-frequency noise from the input. However, capacitors absorb the high-frequency components as their impedance is inversely proportional to frequency according to
with C being the capacitance and with the frequency f in Hz. This can lead to extensive heating and decreased lifetime (up to 40%) of those components, resulting in degradation of the equipment itself [
20].
Furthermore, (linear) load-flow models that are useful for modeling the behavior of “classic” harmonics are not accurate enough to model the propagation of supraharmonics because they are often not directly linked to the fundamental frequency and their behavior in grids is difficult to predict. Interaction between the grid and EMC filters influences the amount of current absorbed by other devices and changes resonant frequencies [
21].
2.2. Sources of Supraharmonics
There are different sources of supraharmonic emissions. In general, all devices with converter-based power electronics emit supraharmonics to a certain extent, as an artifact of the conversion from AC to DC or vice versa. In this research, only the effects on the power quality at the AC side are presented. Nevertheless, effects on the DC side can be present but fall outside the scope of this research.
By switching between grid and microgrid mode, the grid impedance Zg and background distortion in the voltage change. This can lead to a change in the emission of each connected device. Furthermore, it is assumed that the inverter impedances ZPV and Zbat are not constant for the different operation modes. This makes modeling difficult.
For low-voltage networks, the resistance is dominating, especially close to equipment. Hence, for low frequencies (<2 kHz) it can be assumed that Zg is largely resistive. However, for higher frequencies the reactance of the cable will increase and can become dominant and the influence from impedances of neighboring equipment can play a role due to their capacitive nature.
Adding extra devices will create a different impedance seen by the device and will possibly affect supraharmonic emission. However, it is important to note that for each frequency, this model has different parameters, as device impedances (often capacitive due to filters) and grid impedances (often inductive due to cable and transformer characteristics) change with frequency. By superposition of all individual harmonic load-flow models per frequency, the total supraharmonic emission to the grid from the system can be determined. In this linear model, no interaction between devices or other effects are included.
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