Investigations Into Pulsed Transformer Core Material Behaviors
Dawson Wright, Texas Tech University
Modeling magnetic core saturation has been of interest for various pulsed power topologies, such as those using linear transformer drivers (LTD). An extensive 3D Finite Element Method (FEM) analysis of FINEMET cores using Maxwell ANSYS is presented, aiming to align the computational model closely with experimental results obtained under varying magnetization rates obtained with voltage pulses of ~ 10 nanosecond rise times and ~ 1-microsecond duration. The study aims to elucidate the experimentally well-known widening effect of the hysteresis curve under high-frequency or pulse applications by exploring a range of model parameters, such as core conductivity, solid vs. laminations, etc., that best match the experiment.
The more successful approach employs the “effective conductivity†(σeff) to simulate the hysteresis shift away from a DC curve in the magnetic core due to eddy currents in the core accompanied by ohmic core losses. While this method does not resolve laminations, it relies on adjusting σeff to closely match the experimental hysteresis curve for a base set of magnetization rate data. A practical conductivity value of 10 S/m using a solid core approximation closely matched that of an experimental laminated FT-3KL core with the pure magnetic material at 833 kS/m conductivity and a thin oxide layer of insulation between laminations assumed < 0.001 S/m. Keeping all simulation core properties constant, the quality of the match is then reasonably maintained for higher applied voltages corresponding to various magnetization rates, facilitating a direct comparison with the experimental data over a broader range.