An improved calculation of ferrite core loss for nonsinusoidal waveforms separates a flux trajectory into major and minor loops via a new recursive algorithm. It is highly accurate and outperforms two previous methods for our measured data. The only characteristics of the material required are the standard Steinmetz-equation parameters.

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Accurate prediction of ferrite core loss with nonsinusoidal waveforms using only Steinmetz parameters

This paper discusses the influence of nonsinusoidal flux-waveforms on the remagnetization losses in ferro- and ferrimagnetic materials of inductors, transformers and electrical machines used in power electronic applications. The nonsinusoidal changes of flux originate from driving these devices by nonsinusoidal voltages and currents at different switching frequencies. A detailed examination of a dynamic hysteresis model shows that the physical origin of losses in magnetic material is the average remagnetization velocity rather than the remagnetization frequency. This principle leads to a modification of the most common calculation rule for magnetic core losses, i.e., to the "modified Steinmetz equation" (MSE). In the MSE the remagnetization frequency is replaced by an equivalent frequency which is calculated from the average remagnetization velocity. This approach allows, for the first time, to calculate the losses in the time domain for arbitrary waveforms of flux while using the available set of parameters of the classical Steinmetz equation, DC premagnetization of the material, having a substantial influence on the losses, can also be included. Extensive measurements verify the modified Steinmetz equation presented in this paper.

Calculation of losses in ferro- and ferrimagnetic materials based on the modified Steinmetz equation

An accurate power loss model for a high-efficiency dual active bridge converter, which provides a bidirectional electrical interface between a 12-V battery and a high-voltage (HV) dc bus in a fuel cell car, is derived. The nominal power is 2 kW, the HV dc bus varies between 240 and 450 V, and the battery voltage range is between 11 and 16 V. Consequently, battery currents of up to 200 A occur at nominal power. In automotive applications, high converter efficiency and high power densities are required. Thus, it is necessary to accurately predict the dissipated power for each power component in order to identify and to properly design the heavily loaded parts of the converter. In combination with measured efficiency values, it is shown that conventional converter analysis predicts substantially inaccurate efficiencies for the given converter. This paper describes the main reasons why the conventional method fails and documents the different steps required to predict the power losses more accurately. With the presented converter prototype, an efficiency of more than 92% is achieved at an output power of 2 kW in a wide input/output voltage range.

Accurate Power Loss Model Derivation of a High-Current Dual Active Bridge Converter for an Automotive Application

An extension to the Steinmetz equation is proposed, to enable estimation of hysteresis losses in magnetic core materials with nonsinusoidal flux waveforms The new formulation is shown to avoid anomalies present in previous modified-Steinmetz-equation calculations of loss with nonsinusoidal waveforms Comparison with experimental measurements in MnZn ferrite shows improved accuracy The result may be optionally formulated in terms of an effective frequency and an effective amplitude, and options for defining these are discussed

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Improved calculation of core loss with nonsinusoidal waveforms

THIS paper explores opportunities and challenges in power conversion in the VHF frequency range of 30-300 MHz. The scaling of magnetic component size with frequency is investigated, and it is shown that substantial miniaturization is possible with increased frequencies even considering material and heat transfer limitations. Likewise, dramatic frequency increases are possible with existing and emerging semiconductor devices, but necessitate circuit designs that either compensate for or utilize device parasitics. We outline the characteristics of topologies and control methods that can meet the requirements of VHF power conversion, and present supporting examples from power converters operating at frequencies of up to 110 MHz.

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Opportunities and Challenges in Very High Frequency Power Conversion

This paper presents a practical method for predicting the core losses in magnetic components for an arbitrary shape of the magnetizing current. This theory is based on a weighted time derivative of the magnetic flux density and offers the possibility to use the suppliers data, normally derived from measurements with sinewave currents, also for the real current shapes occurring in switch mode power supplies. By means of a special full-bridge power converter, a test setup is developed that allows the verification of the equations derived in this paper.

Calculating core losses in transformers for arbitrary magnetizing currents a comparison of different approaches

In many power electronic applications, ferrite cores of magnetic components are biased with a DC or low-frequency premagnetization. Usually however, the influence of the bias on the losses and permeability is not considered in the component design. This paper describes a precise measurement setup to determine the power losses and the magnetization curve of premagnetized ferrites. The measurements on typical ferrites of two major manufacturers prove that the influence of a DC-bias on the material properties cannot be neglected.

Experimental evaluation of the influence of DC-premagnetization on the properties of power electronic ferrites

Calculation of Losses in Ferro- and Ferrimagnetic Materials Based on the Modified

Ferrite cores of magnetic components used in power electronics are often biased with a DC or low frequency premagnetization. Work has shown that a bias field may have significant influence on the remagnetization losses and therefore has to be considered in the component design. Using a precise measurement setup this paper investigates the frequency dependence of the power loss increase due to premagnetization. The measurements are performed on typical ferrites of two major manufacturers. The experimental results show that there are two major contributions to the total remagnetization losses of soft-ferrites whereas only one contribution is influenced by premagnetization. Finally the paper discusses some aspects of a mathematical description for the bias problem and leads to an improved understanding that might be useful for the designer of magnetic components.

A. Brockmeyer

Papers

Calculation of losses in ferro- and ferrimagnetic materials based on the modified Steinmetz equation

Calculating core losses in transformers for arbitrary magnetizing currents a comparison of different approaches

Experimental evaluation of the influence of DC-premagnetization on the properties of power electronic ferrites

Calculation of Losses in Ferro- and Ferrimagnetic Materials Based on the Modified

Frequency dependence of the ferrite-loss increase caused by premagnetization