Characteristic Analysis of Near-fundamental-frequency Oscillations in a PMSG/ PV Integrated System via MMC-HVDC Considering Multitype Dominant Modes

Recently, a new-type 40~60Hz near-fundamental- frequency oscillation has been observed in PMSG/PV integrated systems via MMC-HVDC. The causes and characteristics remain unclear, posing great challenges for conducting deep research on oscillation control. Focusing on this gap, a state-space model for the PMSG/PV integrated system via MMC-HVDC is built in this paper first. Secondly, potential near-fundamental-frequency dominant oscillation modes of the system are explored by considering the typical ranges for control parameters of the outer loop as well as the inner loop and phase-lock loop of power converters. Then, based on the root locus and participation factors, it is found that there exist two types of near-fundamental-frequency dominant modes. One mode is strongly associated with the dynamics of phase-lock loops of PMSG/PV converters, while the other is strongly correlated with the dynamics of DC voltage outer loops. Besides, both types of modes are highly correlated with the dynamics of the AC voltage outer loop of the MMC. The setting of integral coefficients of the strongly correlated control loops is the root cause of the oscillation occurring at frequencies near the fundamental frequency. Finally, the effectiveness of the conclusions obtained is verified through time-domain simulation.