Impedance measurements from 1–20 MHz with up to 200 A (50 Hz) bias-current for the optimization of high power high frequency coils

Accurate impedance measurements of large coils (largest edge about 30 cm) above 3 MHz are still a challenge. Nevertheless, for the design of filters for conducted emissions up to 30 MHz in high power operations these dimensions are typical. Furthermore reliable characterization of such coils is mandatory for an efficient filter design. However, this topic is hardly addressed in the literature. In this paper, proper measurement techniques are presented to evaluate the impedance, resonances and parasitic effects of very large coils up to 30 MHz. Moreover, a setup is presented to enable measurements up to 20 MHz in on-load operation with 50 Hz nominal currents up to 200 A. This incorporates the issue that the filter performance can change significantly in operations, especially if ferromagnetic core materials are used in the coils.