Spectral Analysis of Photovoltaic Inverter Current Under Harmonic Grid-Voltage Waveform Distortions

In the context of Photovoltaic (PV) installations, power quality is a largely discussed topic and reports on several disturbance events related to PV inverters exist. Respective frequencies cover a broad range and occur in the harmonic, sub-, and interharmonic regimes. To account for the diversity of reported frequencies, we analyze PV-related power quality impairments on a spectral level. Our hardware setup allows investigations of inverters in grid-tied conditions. We contribute three real-world-inspired test cases to evaluate the inverter current under distorted supply conditions. Our observations confirm that the current of a grid-following inverter reflects harmonic distortions imprinted onto the supply voltage known as the auto-sensitivity effect. The analysis presented in this work additionally includes both harmonic and interharmonic subgroups and shows that the influence is limited to a narrow frequency band and does not extend into the neighboring interharmonic frequencies. Both imprinted distortions as well as setup-related background are taken into account. To prevent further degradation of power quality, PV inverters should use an internal ideal sine wave reference for set-point definition rather than replicating the voltage waveform. Inverter-related investigations should maintain a spectral perspective of both voltages and currents to account for frequency-sensitive and setup-related behavior.