Fe based Nanocrystalline Cores for High Voltage

Fe-based Nanocrystalline (FE-N) cores are widely used in power electronicsand pulsed power applications. In pulsed power applications, it always requires high excitation current (up to tens of kA) to excite large-volume cores (up to hundreds of cm3) with fewer number of winding turns, and it is hard to use the traditional test scheme to obtain the pulse magnetic properties in this case. The principles and scopes for the application of pulse magnetic properties measurement circuits, including the single-winding test circuit and double-winding test circuit, are analyzed and presented. Although the double-winding test circuit is classical to test the hysteresis loop, the single-winding test circuit is not totally useless in some cases.

Based on the double-winding test circuit, the initial magnetization curves and maximum hysteresis loops of toroidal FE-N cores with high and low remanence are obtained under a relative constant magnetization rate with the order of 0.7-7 T/μs, and an equivalent frequency from 49 kHz to 650 kHz. The unsaturated permeability is calculated based on the experimental results, and fitted with the magnetization rate. The loss densities and permeability are fitted and compared. A design procedure of the saturable pulse transformer is illustrated for the application of the testing results. It is proved that the initial energy loss and unsaturated permeability are used for the design of the pulse transformer, and the traditional core loss is suitable for the estimation of power loss under the repetitive operation condition.