PhD student

Power Quality & Electromagnetic Compatibility (EMC) in smart grids

Improved performance of LV grid behaviour due to HF emission compensation and attenuation

Context : emerging aspects of electromagnetic compatibility and power quality in low-voltage electricity distribution grids

The low-voltage (LV) electricity distribution grids undergo nowadays a major transformation, due to the expansion of renewable energy sources (RES), local storage, electric vehicles (EV), LED lighting and the presence of other devices powered by switching power electronics. These lead in fact to new Power Quality (PQ) and Electromagnetic Compatibility (EMC) problems. Due to the switching power electronics, the grid voltage and current contain, next to low-frequency harmonics (frequencies less than 2 kHz), an increasing content of power conversion harmonics (PCH) in a higher frequency range up to 150 kHz and above. Moreover, both RES, grid connected inverters (GCI) and loads comprise both switching non-linearities and a non-negligible capacitive behaviour. Consequently, the characteristics of the grid evolves from resistive-inductive into resistive-capacitive, creating low impedance paths for the PCH. Therefore, these harmonics circulate in the LV grid, possibly causing several EMC problems. In addition, due to these new elements, the LV grid is characterized by a continuously changing impedance behaviour, making predictability more challenging. The mutual interactions between switching devices and the grid modify the system behaviour, influence the overall voltage quality, and possibly decrease the grid robustness and the reliability of the connected devices. Moreover, dedicated signalling over the grid, i.e. power line communication (PLC) and ripple control (RC), are possibly strongly affected.

There is still an important standardization gap in this frequency range.

The project strives to build a clear knowledge base on this high frequency (HF) distortion and formulate appropriate mitigation measures. As harmonics are an established problem in many modern applications, the project outcomes can serve a broad range of stakeholders, including (1) manufacturers of power electronics equipment, who should minimize the harmonic content of their products by design, (2) grid service providers, responsible for a proper lay-out of the local network, and (3) other service providers, requiring uncorrupted data and communication to ensure robust operation, (4) standardization bodies and their stakeholders currently working on the frequency band under concern.

The general objectives of the project can be summarized as:

• Contribution to deep understanding of the interactions between new generation power electronics converters and the LV distribution grid,
• Development of innovative and robust filter concepts to mitigate HF interferences in the LV grid, taking into account PLC signals & non-linear loads, with the goal to improve the performance and reliability of the grid.

The project, funded as a Flux50 Strategic Basic Research (cSBO) by the Flanders Innovation & Entrepreneurship agency (VLAIO), is a collaboration between two universities: UGent and UCLouvain.

Description of the proposed research position

The proposed research will mainly focus on the first objective listed above: the understanding, characterization, specification and modelling of the harmonic voltage and current profile (up to 150 kHz) of the LV renewable energy sources and actual (and future) loads. A definition of typical loads and sources will be needed. The targeted result will be several models to simulate the behaviour related to harmonics (including interactions between low- and high-frequency components) under varying power supply voltage and background distortion. A second result will be a substantiated prediction of emission behaviour. The models will be validated through experimental results obtained on a test micro-grid.