Fault Security Region Modeling and Adaptive Current Control Method for the Inverter Station of DC Transmission System

Line-commuted converter-based high-voltage direct current (LCC-HVDC) has undergone extensive development in power systems. Commutation failure (CF) in LCC-HVDC poses a considerable threat to the safe and stable operation of power systems. The coupling of electrical quantities, including DC current, DC voltage, AC voltage, and extinction angle (EA) of an inverter station, is a critical factor that makes CF difficult to suppress effectively. Existing methods adopt preset fixed control parameters and a single control target. The demand of CF recovery typically cannot be satisfied. Control even becomes the driving force of subsequent CF (SCF). Accordingly, a new concept of a fault security region (FSR) in an inverter station under the effects of multi-electrical quantities is proposed. The security range under the coupling effects of electrical quantities is described by the active power and exchanged reactive power of the inverter station. EA, active power, and exchanged reactive power are coordinated through the adaptive regulation of DC current. Thus, SCF can be prevented under the condition that the effect of varying active power and reactive power of LCC-HVDC on a power system is balanced. First, the coupling characteristics of multi-electrical quantities of the inverter station are analyzed. Second, the modeling method for the FSR in the inverter station is proposed. Third, an adaptive current control method is developed by analyzing the evolution characteristics of the FSR. Moreover, a calculation method for the DC current order value is presented. Finally, the effectiveness of the proposed method is verified using the CIGRE HVDC standard system.