Research on controllable series resistance for suppressing commutation failure in high voltage direct current transmission systems

Aiming at the commutation failure problem in high-voltage direct current (HVDC) transmission systems, a solution based on controllable series resistor (CSR) is proposed. This scheme omits the power frequency transformer compared with the existing commutation failure defense module. If the provided auxiliary voltage amplitudes are the same, it requires half the number of power devices compared with the bridge-type controllable series capacitor. Firstly, the topology and control of CSR are given. Then, based on the quasi-steady-state equation, the commutation failure suppression mechanism and control characteristics of CSR are analyzed. The results show that the series resistor at the AC outgoing line can increase the commutation voltage amplitude and suppress the phase-leading jump, which is conducive to smooth commutation. Next, the results of loss analysis show that the steady-state power loss of CSR only accounts for 0.045% of the rated DC power, having little impact on the normal power transmission of the system. Finally, the simulation results based on the PSCAD/EMTDC electromagnetic transient model verify the effectiveness of the proposed scheme: the commutation failure suppression ability of CSR is $\mathbf{6}$ to 7.2 times higher than that of the standard system and 80% to 90% higher than that of the bridge-type controllable capacitor.