An Enhanced Voltage Correction Control Strategy for Asymmetrical Fault Ride-through of Offshore Wind Power Using MMC-HVDC

For the offshore wind power using multilevel modular converter (MMC) based high voltage direct current (HVDC) system, in the case of sending-end asymmetric faults, the offshore MMC generally uses auxiliary positive sequence voltage correction control to prevent overvoltage in the healthy phase. However, due to over-adjustment of the MMC AC voltage reference value, this control can lead to significant reduction in the HVDC system active power transmission capacity when the voltage drop depth is large. Therefore, this paper proposes an enhanced MMC voltage correction control based on nonlinear droop control, adopting the per unit value of the MMC valve-side voltage positive sequence component as the droop coefficient to alleviate the over-adjustment problem in the AC voltage during the fault period. So that the adverse effects of HVDC active power transmission drop on onshore AC grid can be mitigated. The feasibility and superiority of the proposed method were verified through
${\mathbf{PSCAD}}/{\mathbf{EMTDC}}$
simulation cases, which can achieve overvoltage suppression and fault-ride through (FRT).