The low-voltage grid is undergoing a major transformation due to the expansion of renewable energy sources, local storage, LED lighting and other devices controlled by switching power electronics. This leads to new power quality problems. Due to switching power electronics, the mains voltage and current contain more and more power conversion harmonics between 2 and 150 kHz. In the past, electromagnetic compatibility standards were already established for the permitted behaviour below 2 kHz (household equipment) and above 150 kHz (antennas). This intermediate range is now increasingly used for communications (power line communications and ripple control) which are then disrupted, but can also be harmful to other household equipment if there is too much interference. In order to assess and mitigate the impact of medium frequency interference on the low voltage grid, the consortium will model the grid with sources and non-linear loads in this range and investigate innovative and robust filters to improve the performance and reliability of the grid.
The project has two concrete research objectives. On the one hand, a model that correctly represents the impact of the emissions of various components in the frequency range between 2 and 150 kHz needs to be investigated. Hereby, the emission behaviour of renewable energy sources and loads in non-ideal supply conditions, the grid impedance and resonance of net topologies and models of basic grid components are examined. This will result in a robust model with an accuracy of over 90% that will be validated in the test setup at the Lemcko lab.
On the other hand, the project focuses on the investigation of power quality filters that can cope with the disturbances in the frequency range 2 to 150 kHz under changing mains impedance. The optimal filter topology, mains impedance and load impedance are studied for active filters both for one phase and for three phases. The research results in a single-phase medium frequency power quality filter with an attenuation of the noise of the power conversion harmonic of at least 30 dB.