Security domain modeling and suppression of commutation failure for LCC-HVDC considering AC-DC coupling

Abstract

In line-commuted converter based high voltage direct current (LCC-HVDC), commutation failure (CF) is a main source of danger. The CF is usually suppressed by regulating the single electrical quantity. However, for the active and reactive power of inverter station, the combination of DC current and voltage, AC bus voltage, firing angle (FA) and extinction angle (EA) is the determining influence. The regulation of any electrical quantity leads to variations in power, thereby influencing the AC bus voltage and subsequently inducing variations in the DC current, DC voltage, and EA. The neglect of AC-DC coupling affects the suppression of CF and limits power transmission. The formulation of the active and reactive power of inverter station has been deduced. Considering the constraints imposed by DC current and firing advance angle (FAA), the power feasible range is established. The feasible range of AC bus voltage and power is built considering AC-DC coupling. The commutation security domain of inverter station to avoid CF is modeled. To maximize the active power, formulations of DC current and FAA are proposed. Taking into account the power transmission, an improved suppression method of subsequent CF is proposed. The CIGRE standardized model is utilized to verify the method.