Protection of Multi-Terminal VSC-HVDC Grids Based on the Response of the First Carrier Frequency Harmonic Current

Protection of multi-terminal Voltage Source Converter based High Voltage Direct Current (VSC-MTDC) grids is a major challenge for future practical DC transmission technology. According to the harmonic-based protection studies, the response of first carrier frequency harmonic (FCFH) current in Pulse Width Modulation (PWM)-based VSC-HVDC can be used to discriminate external AC faults in point to point VSC-HVDC systems. However, the application of FCFH current for a selective fault detection system in VSC-MTDC grids is not studied yet. This research investigates FCFH current existed in converter DC link measured data, to detect the faulty section in VSC-MTDC system, when the system face faults with variations in location and resistance. A radial VSC-MTDC system with 2-level PWM VSC converters is simulated in PSCAD and MATLAB is used to extract FCFH current based on short-time Fourier transform. Based on the relay locations, the results show the feasibility of the protection algorithm, in discriminating between internal and faults for each zone.