Interaction of low-voltage grids with Active Front Ends

In the foreseeable future limit values for conducted emissions of Active Front Ends in the frequency range of 2 kHz to 9 kHz will exist. Recent studies on the conditions at low-voltage mains were not yet available. Therefore in this thesis low-voltage mains are investigated. At different locations and mains the impedances as well as the harmonics are measured. A large database was created and it is evaluated statistically. These results of the work have been incorporated into the technical specifications [34] and served there as a reference value for definition of limits for concucted emissions.

Based on these impedance networks for simulations and a real Line Impedance Stabilisation Network are designed beyond. These reflect the impedances at real low voltage mains. the Line Impedance Stabilisation Network has been implemented and is verified by measurements.

Furthermore, is is examined how the conducted emissions of Active Front Ends can be reduced. Objective here is to achieve a cost-neutral reduction in both the single and parallel operation.

For stand-alone operations, a controller is designed with adjustable dynamics. It manages an analytical description of the overall system. Thereby, the influence of all relevant variables is examined for the behavior of the entire system. Is is shown that the conducted emissions of an Active Front End can be reduced by appropriate control design.

In parallel operation, the conducted emissions of Active Front Ends can be reduced significantly. Is is shown that in case of spatially concentrated systems a cancellation of harmonics is possible by suitable modulation.