A Low‐Intrusive Electric‐Field‐Coupled Voltage Sensor for Terminal Voltage Measurement of MMC Submodule

ABSTRACT

Terminal voltage of MMC valve assemblies is a key parameter for condition monitoring in flexible high‐voltage direct current transmission systems. However, the compact layout and severe electromagnetic interference in high‐potential regions make conventional contact‐based measurement susceptible to loading effects and safety risks. This paper proposes a low‐intrusive electric‐field‐coupled voltage sensor for terminal voltage measurement of MMC valve assemblies. An ideal capacitive model and an interference coupling model are established to derive the frequency response characteristics of the proposed sensor and analyse the mechanism of external electric‐field interference. A four‐layer printed circuit board sensing electrode with a bowl‐shaped shielding structure is designed, reducing the simulated interference coupling ratio from 10% to 1.64%. In addition, a parameter design method based on the matching relationship between the coupling capacitance and the lumped capacitance is proposed to realise proportional output in the self‐integration mode. Double‐pulse experiments show that the maximum position‐induced transfer‐ratio deviation of the shielded sensor is 2.36% under the three investigated installation conditions. The proposed method demonstrates the feasibility of low‐intrusive terminal‐voltage sensing for further application to MMC submodules.