Abstract:

In view of the scenario of disturbance at the receiving end of offshore wind power through MMC-HVDC system, this paper proposes an adaptive control strategy to ensure the operation of the receiving-end converter station within the non-hazardous range independently and realize the reasonable distribution of active power among multiple sending-end converter stations. It includes the operating limit control strategy of the receiving-end converter station and the U_dc-f adaptive droop control strategy of the sending-end converter station. When the disturbance of receiving-end power grid leads to over-limit of internal electrical variables in the receiving-end converter station, the operating limit control will output the reduction coefficient to reduce the reference value of virtual potential, so that the internal electrical variables will return to the limit value. The adaptive droop control strategy is to adjust the droop coefficient adaptively under the constraints of active power margin and DC voltage deviation, so as to reasonably distribute the disturbance power among multiple sending-end converter stations adjusted by the wind farm due to the receiving-end disturbance and reduce the DC voltage deviation. The control strategy of sending-end and receiving-end works together to maintain whole system stability. Finally, a three-terminal MMC-HVDC simulation model is built in PSCAD/EMTDC to verify the effectiveness and accuracy of the proposed method.

Key words: wind farm, MMC-HVDC, receiving-end disturbance, constraint condition, adaptive control, adaptive droop control, operating limit control