A single-ended fault location method for DC lines in bipolar MMC-HVDC system

Fault location of DC grid is one of the crucial techniques for safe and reliable operation of power systems. This paper presents a single-ended fault location method for DC lines in bipolar high-voltage direct current transmission based on modular multi-level converter (MMC-HVDC) system, which focuses on short-distance DC lines. Firstly, the fault path after tripping is considered to be equivalent to a two-order RLC series circuit, and the initial voltage of the fault path is provided by the residual voltage of MMC submodule capacitors. Then, the differential equation of the fault path is established in time domain. Finally, by sampling the voltage and current signal of single-end MMC submodule capacitor and the voltage signal of the MMC bridge arm inductor, the fault distance, as well as the fault resistance, is obtained. A bipolar MMC-HVDC model is built by PSCAD/EMTDC, and the proposed method is verified by MATLAB. The simulation results show that the proposed method can accurately locate the fault position and is almost immune to the fault resistance.