Research on DC-Side Impedance Measurement Method for Flexible HVDC Converter Stations Based on Modulation Index Injection Perturbation

Aiming at the impedance measurement requirements for the direct current (DC) side of flexible DC converter stations, this paper proposes a novel impedance measurement method based on modulation index injection perturbation. Unlike traditional impedance measurement approaches, the proposed method eliminates the need for external impedance measurement equipment, thereby addressing issues of high costs and installation inconveniences while enhancing overall system efficiency and reliability. The novel measurement technique is further integrated with Sliding-window Discrete Fourier Transform (SDFT) to enable real-time extraction of perturbation components in DC voltage and current. Combined with Ohm’s law, this integration facilitates efficient calculation of wide-frequency impedance characteristics and improves impedance measurement efficiency. Finally, the effectiveness and efficiency of the proposed measurement method were validated through MATLAB/Simulink platform simulations.