Bipolar Short Circuit Fault Location Method for Flexible DC Grid Based on Active Current Injection

A fault location method for flexible DC power grid based on active control of fault current is proposed. Based on the high controllability of hybrid MMC, the fault current is divided into two stages: S
1
and S
2
. Stage S
1
is mainly used to realize fast suppression of fault current and provides conditions for smooth transition of stage S
2
. In stage S
2
, the fault can be accurately located by injecting reverse sinusoidal current with specific frequency. This paper firstly takes the asymmetric "hand in hand" flexible DC grid as a typical topology to analyze the rising rate of fault current in the initial stage of DC fault, and then a fault current reference signal is designed based on the characteristics of initial fault current. Next, it introduces the fault location principle and corresponding fault location process of stage S2. Finally, it builds a simulation model of ± 10kV /21 level two terminal DC power grid in PSCAD/EMTDC to verify the accuracy of fault location. Compared with other location methods, the simulation results show that this method has a better ability of anti-noise interference and fault resistance. Morever, not only is this method economical, but also the location error of it is stable within 1.5%.