A Novel Control Strategy for Suppression of Transient Overvoltage and Subsequent Commutation Failure for LCC-HVDC

For an LCC-HVDC, the commutation failure (CF) of the inverter will cause the transient overvoltage (TOV) in sending-end system, while the existing control strategies based on the DC controller will increase the risk of subsequent commutation failure (SCF). To handle this problem, the interactive coupling among DC current, converter bus voltage of the inverter side, and advanced firing angle of the inverter side is analyzed, and reveals that the coupling between electrical and control quantities leads to the intertwining of TOV with SCF. The interactive coupling between electrical and control quantities is decoupled, and the mathematical equation for extinction angle variations and DC current changes is established by Taylor series expansion method. The SCF risk index (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SCFRI</sub>) is proposed to achieve the effective identification of the risk of the SCF, on this basis, a novel control strategy for suppressing TOV and SCF is proposed. The proposed control strategy can also enhance the DC recovery speed. Finally, the CIGRE HVDC Benchmark Model in PSCAD is built, and the simulation results with different working conditions indicate that the novel control strategy can suppress the TOV and SCF with good recovery performance.