Harmonic Emissions in 0-9 kHz Frequency Range and Transient Effects in Grid-Connected Inverters Utilised in Solar Farms

The penetration level of large-scale inverters utilized in solar farms is continuously increasing. A large part of PV power generation comes from large-scale and high-power inverters, which are normally connected to the grid through a distribution transformer. The operation of these high-power inverters with switching frequency mainly below 9 kHz due to design constrains need to be studied and their short-term incidents need to be understood. For that purpose, in this paper, output currents of three inverters have been measured using field measurements of a 3MW solar farm. The currents are then analyzed in time and frequency domains. The results show large short-term DC current and significant harmonic emissions (0-9 kHz) during short period of times, while the steady-state harmonic levels do not seem to be significant.