A New Online Power Reversal Strategy for LCC-HVDC Systems Utilizing Round Power Mode

Achieving higher renewable penetration in power systems requires more operational flexibility due to the variability of renewable energy sources. LCC-HVDC systems, boasting the largest installed capacity among existing HVDC technologies, hold tremendous potential to offer grid flexibility through their strong power control capabilities. However, LCC-HVDC systems suffer from the inherent issue of uncontrollability at low power levels, fundamentally limiting their application in providing the much-needed grid flexibility. To address this issue, this paper proposes a new online power reversal strategy for LCC-HVDC based on round power mode (RPM). The proposed strategy can achieve continuous control at low power levels and unlock the full flexibility of LCC-HVDC. Then the detailed modelling of the proposed strategy including power reversal process, mode-switching methods and coordinated operation of bipolar units are presented in this paper. The simulation results using PSCAD/EMTDC demonstrate the performance of the proposed strategy across all power levels.