Harmonic Emissions in Microgrids

Sammanfattning: “Affordable and clean energy” is EUs 7th Sustainable Development Goal and includes an increase of renewable energy generation in the global energy mix. A lot of the responsibility falls on the energy sector to transform and obtain solutions for a more sustainable future. The development is going towards decreased decentralized generation and an increased share of renewable energy sources like wind- and solar power. This requires new network systems and technologies with added flexibility and capacity, such as micrograms. This work aimed to analyse current and voltage harmonics in a microgrid where the purpose was to examine if harmonics behave differently in grid-connected mode and island mode and if there is a correlation between weather and harmonics. The purpose was also to see if electrical harmonics can be reproduced in a model of the microgrid in a simulation program and what the limitations of such a simulation are. The microgrid studied was developed by E.ON and contains a wind turbine, photovoltaic panels, a backup generator, battery energy system and loads. The microgrid was disconnected from the distribution grid at limited times during the project. This thesis work was limited to only having the wind turbine and PV panels as harmonic sources. In order to develop this work, the method chosen was to analyse collected microgrid data for various measurement points and weather conditions and then construct a model based on this live system data. The data analysis showed constant current harmonic emission levels independent of the wind speed and irradiation, except for the fifth harmonic at the PV installation. It also showed that the harmonic levels were higher for grid-connected mode than for island mode. The simulated harmonics were smaller than the measured harmonics and therefore, they could not be reproduced in the simulation model. There is no general correlation between weather and harmonic emission levels. The harmonics were higher in grid-connected mode as the harmonics from the distribution grid are added to the microgrid. The simulation was based on only harmonics from the wind turbine and photovoltaic panels. However, the real microgrid has several sources of harmonic emission, which make the measured harmonic values higher than the simulated values.