Grid-tied Inverters in Renewable Energy Systems: Harmonic Emission in 2 to 9 kHz Frequency Range

Abstract

Grid distortion due to the high switching frequency of energy conversion systems has become a major concern that reduces power quality in renewable energy systems. However, the existing international standards (IEC 61000-3-2&12&16 and IEEE Std. 519) list grid harmonic limitations only up to the 40th or 50th harmonic. Due to limited knowledge of supraharmonic (Harmonics above 2 kHz) currents and voltages, an appropriate standard for this high frequency range is yet to be published. This paper presents an analysis of grid current distortion in the frequency range of 2 to 9 kHz when an active front end inverter is connected to the grid under different filter designs. New filter design approach is used to reduce or eliminate harmonics at frequencies beyond the ranges considered in conventional standards. The results show significant mitigation of high frequency harmonics in stiff grids. High frequency harmonic behavior with conventional and newly designed filters connected to a weak grid, are compared to find small amplitude current and voltage harmonics using the new filters. Furthermore, this study highlights the need for a new standard to address supraharmonics caused by grid-tied inverters.