Research on optimized control strategy for LCC-CLCC Receiving-End under different Degrees of Three-Phase fault conditions

Compared with traditional Line-Commutated Converters (LCCs), the Controllable Line-Commutated Converter (CLCC) exhibits a significantly enhanced immunity to commutation failures. To fully leverage this characteristic and further improve the system’s power transfer efficiency during faults, this paper analyzes the characteristics of the rectifier-side controller and the relationship between the CLCC’s reactive power and its firing angle as well as DC current in an LCC-CLCC system during a three-phase AC fault at the receiving end, so as to facilitate system regulation under fault conditions. Subsequently, a transient expression for the firing angle under fault conditions is derived to calculate its target adjustment value. Utilizing its controllable advantages, a control optimization method based on maximizing the firing angle elevation is proposed for mild AC faults at the receiving end. Furthermore, starting from the commutation area theory of the CLCC, the reasons for its strong immunity to commutation failures are revealed. An optimized Voltage Dependent Current Order Limiter (VDCOL) control strategy that compensates for DC current variations is proposed for severe AC faults at the receiving end. Both control strategies enhance AC voltage support and active power retention capability during faults and accelerate system recovery. Finally, the effectiveness of the proposed control strategies under three-phase short-circuit ground faults is verified through electromagnetic transient simulations using PSCAD/EMTDC.