Temperature-Dependent Magnetic Hysteresis Measurement and Modeling of Soft Ferrites Applied to Power Electronic Transformers

Magnetic core is one of the key components of Power Electronic Transformers (PETs), and its magnetic hysteresis properties is vital for the accurate design and analysis of PETs. In this paper, measurement and modeling of magnetic hysteresis of soft ferrites at different temperatures are conducted. Jile-Atherton (J-A) model is utilized to model the magnetic hysteresis behavior. Firstly, a clarification on the correct form of the anhysteretic magnetization is made. Then, NeIder and Mead Simplex algorithm, a derivative free method, is employed to identify the parameters of the J-A model. A temperature-dependent J-A model is deduced by expressing the parameters as functions of temperature, and Curie temperature Tc and critical exponent β are introduced as the additional parameters. The simulation results and the area enclosed by BH data derived from the J-A model are compared with the measurement. Most of the results agree well with the measurement, the largest relative error is about 18.78^%• Comparisons between the results acquired from the temperature-dependent J-A model and the measurement are made. This temperature-dependent J-A model shows good performance in predicting hysteresis behavior in lower temperature range. However, its performance in predicting hysteresis behavior in higher temperature range is not desired.

1. Introduction

With the rapid development of smart grid and energy internet as well as the renewable energy, such as wind and solar energy, power electronic transformers (PETs) gained more and more attentions, and it has become one of the hot issues. This energy conversion system has many advantages, such as voltage transformation, power quality functions, and power regulation by using power electronics converters on both sides of a medium frequency transformer (MFT) [1] [2]. This MFT could dramatically decrease the volume and weight compared with the traditional transformers by operating in frequency range from several kHz to tens of kHz. The selection of magnetic materials is critical to fulfill the high operating frequency performance. There are 4 different types of magnetic materials commercially available for iron cores of MFTs, namely, nanocrystalline, amorphous, soft ferrites and silicon steels [3]. Because of its high permeability, low eddy current loss, and low cost, soft ferrites are often considered as one of the best candidates of magnetic materials for high-frequency magnetic devices [4]. Though it has many attractive characteristics, soft ferrites are sensitive to the operating temperature. Its saturation flux density at 120°C could be reduced to less than 1/3 of that at 20°C for certain type of soft ferrite. Apparently, thermal effect on the magnetic properties of soft ferrites has become one of the critical issues for performance prediction and optimal design of high frequency magnetic components utilizing soft ferrites due to the need for high switching frequency and high power density magnetic devices in power electronic converters. Magnetic material properties have strong influences on the performance of the MFTs design and behavior prediction. Hence, it is is necessary to study the thermal effect on magnetic hysteresis behavior of soft ferrites.