Magnetics Business & Technology - Spring 2015 - (Page 12)

FEATURE ARTICLE Magnetics Design Tool for Power Applications By Mauricio Esguerra, Dipl. Phys. * Mauricio Esguerra Consulting on behalf of Hengdian Group DMEGC Magnetics Co., Ltd Predicting the behavior of soft magnetic cores under realistic circuit application conditions allows making an optimum material and core selection. This requires visualizing material data of soft magnetic materials, as well as calculating core parameters such as inductance, core losses, transferable power and EMI suppression as well as associated basic winding design parameters. The free app, Soft Power*, uses proven simulation methods such as hysteresis modeling for a reliable design, allowing faster time to market while maximizing engineering resources. lowing heuristic description introducing the squareness exponents aL and aU for the lower and upper curves respectively: (5a) (5b) Figure 1 shows one example of a major loop and a calculated minor loop. Material Parameters Both soft ferrites and powder core materials are featured based on representative ring cores tested according to IEC Standards (IEC 60401-3, IEC 62044-1/2/3). The software shows graphs of relevant parameters for every material grade: * * * * * * Permeability µ vs. temperature, flux density and DC-Bias Complex permeability µ', µ" vs. frequency Small-signal losses (tand/µ) vs. frequency Normalized impedance ZN vs. frequency Power losses Pv vs. frequency/flux density/temperature Hysteresis loops B(H) Hysteresis Modeling In order to accurately simulate high excitation parameters such as power loss and DC-bias at any given condition, hysteresis modeling is necessary. The use of models such as the Steinmetz power equation[1] have limited validity in the frequency, flux density and temperature ranges; extrapolating these limits can result in very large errors due to the exponential nature of the equation. The hysteresis models based on Hodgdon's differential equation[2] naturally overcomes these limitations[3]. By regarding the measured major hysteresis loop as a particular solution to the equation, the upper and lower branches of a minor loop between the end points (Hm, Bm) and (HM, BM) can be described as a function of the upper and lower curves of the major loop: Figure 1. Major loop for material DMR47 at 80°C. The symmetric minor loop was calculated for -Bm = BM = 200 mT. Derived Parameters The calculation of application relevant quantities is straight forward. Loss energy for a symmetric loop of amplitude BM is obtained by integration and can be approximated for small flux densities as follows: (6) (1a) (1b) With The expression for the reversible permeability µrev vs. Bdc contains two different terms, the first related to losses and the second related to squareness (a= aL=aU): (7) and the commutation curve (4) Where Hc is the coercivity, µc its permeability and Bs the saturation flux density. In addition to these parameters the model requires the knowledge of the initial permeability µi, which is also a well-defined quantity. The measured major loop curves can be parametrized by the fol- Temperature Dependence The hysteresis parameters are determined for major loops tested at different temperatures. In order to allow the software to calculate related quantities at a given temperature, the five hysteresis model parameters are fitted as a function of temperature. * Download from (requires Java JRE 1.6.0 or higher) 12 Magnetics Business & Technology * Spring 2015

Table of Contents for the Digital Edition of Magnetics Business & Technology - Spring 2015

Editor's Choice
First-Order-Reversal-Curve Analysis of Multi-Phase Ferrite Magnets
Magnetics Design Tool for Power Applications
Magnet Inspection Tool with High Magnetic and Mechanic Accuracy
Research & Development
Software & Design
Industry News
Marketplace / Advertising Index
Spontaneous Thoughts: The Patent Challenge

Magnetics Business & Technology - Spring 2015