Forced oscillation in hybrid system with grid-following and grid-forming inverters

Song Chen, Yang Wang, Mengling Yang, Xianyong Xiao and Oriol Gomis-Bellmunt

Energy, 2025, vol. 319, issue C

Abstract: This paper identifies a new oscillation phenomenon in hybrid systems composed of grid-following (GFL) and grid-forming (GFM) inverters. Different from the existing work that mainly focuses on the natural oscillation, this paper discusses a kind of forced oscillation (FO), where the GFL inverter serves as an excitation source to force GFM inverters oscillating. The study demonstrates that when the maximum power point tracking (MPPT) frequency is four times the low frequency oscillation (LFO) mode frequency of the GFM inverter, the interharmonics generated by MPPT can excite the LFO mode. As a result, the power disturbance component in the GFL inverter is amplified by more than sixfold in the power components of the GFM inverter. The phenomenon is some-what similar to the FO in traditional power systems. In this paper, the power source characteristic of injected interharmonics is first revealed. Taking advantage of this feature, the mathematical expressions of FOs can be analytically derived, enabling accurate prediction of the amplitude of the FOs. Afterwards, the characteristics of FOs as well as the influence of various factors, such as MPPT frequency, capacity ratio, and resistance to inductance ratio are investigated. Finally, hardware in the loop tests are employed to validate this phenomenon in a hybrid system consisting of a GFL controlled PV farm and a GFM controlled battery energy storage system.

Keywords: Forced oscillation; Grid-forming; Grid-following; Interharmonic; Maximum power point tracking (search for similar items in EconPapers)
Date: 2025
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Persistent link: https://EconPapers.repec.org/RePEc:eee:energy:v:319:y:2025:i:c:s0360544225005572

DOI: 10.1016/j.energy.2025.134915

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