Characteristic Analysis of Quasi-Power-Frequency Sequence Oscillations in DFIG Wind Farms Integrated via MMC-HVDC

The quasi-power-frequency sequence oscillation is a new type of oscillation issue observed in practical renewable energy integrated power systems via MMC-HVDC in recent years. In this paper, characteristics of quasi-power-frequency oscillations in DFIG wind farms integrated power systems via MMC-HVDC are studied. Frist, state-space model of the system is established. Then impact of control parameters on the quasi-power-frequency oscillation is analyzed based on the root locus method. Finally, effectiveness of conclusions drawn based on the linearized model is verified via non-linear simulations. It is found that this new type of oscillation is mainly relative with the dynamics of phase lock loop of the DFIG, current inner loop of RSC of the DFIG and AC voltage outer loop of the MMC. In addition, increase of active power outputs of the DFIGs can also decrease damping of the oscillation.