An improved fault current limiting circuit for VSC-HVDC transmission system

In order to maximize the utility of renewable energy resources, long-distance power transmission lines are essentially required. To accomplish this purpose, the voltage-source-converter (VSC) based high voltage direct current (HVDC) transmission is considered an attractive option. However, due to DC-link capacitors and their discharge currents, the VSC-HVDC based transmission networks are more vulnerable to short circuit faults. The direct current circuit-breakers (DCCBs) are considered a reliable option to protect the transmission line against short circuit faults. The DCCBs with increased voltage rating and fault-current interruption capability are still considered a gigantic problem. The capacity issues of DCCBs can be alleviated using some external circuits to reduce the intensity of fault-current. This paper introduces an external fault-current limiting circuit (FCLC), which is non-superconducting in nature, and it consists of power electronics-based bidirectional switches, current limiting inductor, and power dissipating resistor. This circuit is placed in series with a DCCB, to escalate the response time in the advent of fault, to restrict the maximum value of fault-current, and to reduce the stresses on energy absorption components in DCCB. The circuit is activated only when fault-current limitation operation is required, thereby, the proposed FCLC has zero power-loss in the nonoperational state, and has no influence on the steady-state performance of the system. Furthermore, regarding FCLC, the detailed working principle, parametric analysis, and rigorous evaluation of performance are accomplished in this paper. The theoretical concepts are validated using a three-terminal VSC-HVDC model and equivalent circuit analysis, in PSCAD/EMTDC simulation-based environment. The results of FCLC are compared with other solutions in the literature. The comparison of results concludes that the proposed FCLC own better characteristics, in terms of control features, fault clearing time, and power losses.