Analysis of the Magnetic Field at the Driving Board of the MMC Sub-module of 500kV VSC Valve

Before leaving the factory, the 500kV VSC valve used in the ZhangBei project needs to be subjected to electromagnetic compatibility immunity test for the driver board of its MMC sub-module, including power frequency magnetic field immunity test. In order to determine the level of the test, it is necessary to analyze the magnetic field distribution at the sub-module driving board of the VSC valve. This paper analyzes the transfer process of the current in the sub-module when the 500kV VSC valve is in normal operation, establishes its magnetic field calculation model, and builds a double-pulse test platform. The error of the magnetic field value is less than 10%, which verifies the validity of the model. The model is used to predict the magnetic field waveform characteristics of the sub-module driving board when the 500kV VSC valve has a normal flow of 3kA. At the same time, the magnetic field contribution of the adjacent sub-modules to the central sub-module is analyzed. The results show that the adjacent sub-module is the main contribution of the magnetic field at the drive board, and the effective value of the magnetic field strength can reach up to 900A/m, It is necessary to improve the test grade of power frequency magnetic field disturbance immunity for submodule drive board.