Study On High Frequency Magnetic Loss Model Under DC Bias

Switching converter miniaturization equires us to increase the switching frequency to reduce the size of device,while maintaining the power in the same circumstances.But at the same time,to improve the switching frequency will make that the magnetic components increase in loss rapidly.Heat problems can not be ignored.Accurately estimating the core loss and establishing an accurate core loss model has been a matter of great concern to academia.So establishing a precise and practical magnetic core loss model is signicant for predicting core loss under different circuit topology and different working conditions,power electronic converter thermal design and improving the performance and reliability of switching converters.Obtaining accurate core loss data is also an indispensable part of core losses,which can provide fitting and verification data for the establishment of loss model formulas and loss estimating for engineering applications.Accurate measurement of core losses has been a challenge.The difficulty of measurement has increased greatly,when the frequency and power density of switching converter is increasing.Firstly analyze the causes of core loss in this paper.The characteristics,influencing factors and calculation methods of hysteresis loss,eddy current loss and residual loss are described in detail.Analyze the existence of core loss under different excitation waveforms.The core loss under non-sinusoidal excitation is predicted which is based on the core loss under sinusoidal excitation.the automatic test system of high frequency core loss is established based on the direct measurement method.The system uses virtual instrument technology.The computer controls the instrument in a remote manner to complete the work of data collection.Analyzing the loss data and predicting core losses combined with core loss model and working circuit.Design a high-precision frequency signal generator to support the operation of the automatic test system.Design a soft-start circuit to eliminate the transient process when the signal source generate the signaland turn off the signal.Under different circuit topologies and different working conditions,the relationship between the frequency,duty cycle and DC bias magnetic field of the waveform and the power loss of the magnetic element will change.Previous studies have often neglected the relationship between DC magnetic bias and core loss.In fact,the DC bias magnetic field has a very important effect on the core loss.In this paper,the influence of DC bias magnetic field on hysteresis loss and eddy current loss is analyzed.A simple and practical mathematical model is proposed to predict the core loss under rectangular excitation which is base on the core loss data under sinusoidal excitation with DCmagnetic bias.Power inductor of Buck and Boost converters works in pulse voltage excitation with DC bias.Core loss modeling is very difficult because of its non-linear operating characteristics of the power inductor.According to the physical mechanism of hysteresis loss and eddy current loss and the working characteristics of Buck and Boost converter,a simplified core loss estimation method is proposed.