Analysis of 0.1-Hz Var Oscillations in Solar Photovoltaic Power Plants

Oscillations with very low frequency at 0.1 Hz, have been observed in voltage and var in practical solar photovoltaic (PV) systems when power exporting ramps up to a certain level. This letter provides an explanation on the formation of 0.1-Hz oscillations and identifies three critical factors that lead to the oscillations: communication delay between the plant-level control and the inverter-level control, high volt/var sensitivity at a high power exporting level, and the volt-var feedback system consisting of the plant control, inverter control and the grid impact. Furthermore, a critical feature of the 0.1-Hz oscillation is also explained: why oscillations appear only in voltage and var, but not in real power.

Automated summary

Low-frequency oscillations at 0.1 Hz have been observed in voltage and var in practical solar photovoltaic systems, and this letter provides an explanation for their formation. Three critical factors leading to the oscillations are identified: communication delay between plant-level and inverter-level control, high volt/var sensitivity at high power exporting levels, and the volt-var feedback system involving plant control, inverter control, and grid impact. Additionally, the critical feature of the 0.1 Hz oscillation is explained, which is the absence of oscillations in real power.