Self-Induced and Mutual-Induced Emissions of Grid-Tied Converters

The increased use of grid-tied converters (GTCs) leads to power conversion harmonics in low-voltage networks in the supraharmonic (SH) range. The effect of using grid-tied converters with switching rates that are noninteger multiples of the grid frequency is studied. It is observed that both high-frequency (HF) and low-frequency (LF) emissions increase more than what is expected and occur at many interharmonic frequencies, due to a combination of feedback mechanisms. When a GTC is switched with a noninteger multiple of the grid frequency, extra harmonic bands appear around the main LF and HF harmonics emitted from the GTC. The frequencies of these additional harmonics depend on the deviation of the HF emissions from the nearest integer multiple of the grid frequency. Two definitions are presented, the self-induced emissions that represent the extra HF emissions generated by the device itself and the mutual-induced emissions that define the extra emissions of a device around its switching frequency and its multiples as a reflected effect of the HF emissions of a neighboring device. Simulations using MATLAB software are performed to clarify the results. An experimental setup is used to verify the outcomes with two case studies.