Impact of a power converter virtual impedance based fast fault current injection control strategy on distance protection

An increasing trend in the power system involves the substitution of conventional power units with Voltage Source Converters (VSCs). The fault response characteristics of VSCs are mainly determined by the current rating of its semiconductor device and the control strategy applied to them, which cannot inherently generate a large amount of fault current like traditional synchronous generators. Moreover, with the suppression of negative sequence current under unbalanced conditions, VSCs will affect the apparent impedance seen by the distance relay, thus affecting the distance protection of transmission lines. This paper investigates a Fast Fault Current Injection -Virtual Converter System (FFCI-VCS) control strategy based on a virtual impedance network, which serves two pivotal objectives: firstly, to enable the converter to inject the maximum feasible fault current during the initial 1-2 cycles subsequent to a grid fault event, and secondly, to enhance the operational efficiency of distance protection systems. The performance of the FFCI-VCS is evaluated through Simulink simulations under both balanced and unbalanced grid faults. The outcomes verify its ability to achieve fast fault current injection and diminish the response time of distance relays across various fault types, transmission distances, and fault resistance conditions.