A Study on High-Current Rectifier Systems With Mitigated Time-Varying Magnetic Field Generation at AC Input and DC Output Busbars

This paper investigates occupational exposure to time-varying magnetic field generation in high-power rectifier systems. Two different kinds of high-power rectifier systems rated for 25 kA are modeled and analyzed. The performance is compared and evaluated on the basis of exposure guidelines from the International Commission on Non-Ionizing Radiation Protection (ICNIRP). In order to focus on the qualitative effect of rectifier operation, the mechanical structure of the current-carrying conductors is simplified as an infinite long busbar model and low-frequency harmonic contents up to 65 kHz are considered. A thyristor rectifier generates a significant amount of low-frequency magnetic field harmonic contents, both at the ac and dc sides of the rectifier, infringing the limit from ICNIRP. The multilevel IGCT-type rectifier has almost negligible field generation from the ac input side and smaller harmonic contents in the dc load side, complying with ICNIRP guidelines. This remarkable advantage of multilevel rectifier-IGCT type can lead to a simpler site layout design for installation and cost-effective compliance to the guidelines of occupational exposure against the magnetic field.