This paper addresses a bidirectional dc-dc converter suitable for an energy storage system with an additional function of galvanic isolation. An energy storage device such as an electric double layer capacitor is directly connected to a dc side of the dc-dc converter without any chopper circuit. Nevertheless, the dc-dc converter can continue operating when the voltage across the energy storage device drops along with its discharge. Theoretical calculation and experimental measurement reveal that power loss and peak current impose limitations on a permissible dc-voltage range. This information may be useful in design of the dc-dc converter. Experimental results verify proper charging and discharging operation obtained from a 200-V, 2.6-kJ laboratory model of the energy storage system. Moreover, the dc-dc converter can charge the capacitor bank from zero to the rated voltage without any external precharging circuit.

A Bidirectional DC–DC Converter for an Energy Storage System With Galvanic Isolation

A switching control strategy to control the power flow and minimize the total power losses of the dual active bridge converter topology is proposed in this paper. The control strategy consists of driving the bridge with the largest DC voltage to generate a three-level pulsewidth-modulated (PWM) voltage waveform. This PWM is ruled by two manipulated variables: the phase shift between the primary and secondary transformer voltages and the modulation index. These variables are calculated using an algorithm that is deduced on the basis of particular calculation and analysis of converter losses, which are also presented in this paper. An experimental prototype was implemented to validate the theoretical analysis and feasibility of the proposal. The experimental results revealed that the overall efficiency of this converter can be improved up to 10% using the control strategy instead of the conventional one.

Switching Control Strategy to Minimize Dual Active Bridge Converter Losses

The trend toward high power density, high operating frequency, and low profile in power converters has exposed a number of limitations in the use of conventional wire-wound magnetic component structures. A planar magnetic is a low-profile transformer or inductor utilizing planar windings, instead of the traditional windings made of Cu wires. In this paper, the most important factors for planar transformer (PT) design including winding loss, core loss, leakage inductance, and stray capacitance have individually been investigated. The tradeoffs among these factors have to be analyzed in order to achieve optimal parameters. Combined with an application, four typical winding arrangements have been compared to illustrate their advantages and disadvantages. An improved interleaving structure with optimal behaviors is proposed, which constructs the top layer paralleling with the bottom layer and then in series with the other turns of the primary, so that a lower magnetomotive force ratio m can be obtained, as well as minimized ac resistance, leakage inductance, and even stray capacitance. A 1.2-kW full-bridge dc-dc converter prototype employing the improved PT structure has been constructed, over 96% efficiency is achieved, and a 2.7% improvement, compared with the noninterleaving structure, is obtained.

https://orbit.dtu.dk/files/4566316/Ouyang.pdf

Optimal Design and Tradeoff Analysis of Planar Transformer in High-Power DC–DC Converters

The calculation of core losses in inductive components is difficult and has not yet been entirely solved. In particular, it is impossible to predict the influence of a dc premagnetization on the losses without extensive measurements. For this paper, different materials have been tested to gain information on how core losses are influenced by a premagnetization. Measurements on molypermalloy powder, silicon steel, nanocrystalline material and ferrite cores have been performed. The Steinmetz premagnetization graph (SPG) that shows the dependency of the Steinmetz parameters ( , and ) on premagnetization is introduced. This permits the calculation of core losses under dc bias conditions. Such graphs are given for different materials and different operating temperatures. In addition, a detailed description of the test system is given, as high accuracy is crucial.

Core Losses Under the DC Bias Condition Based on Steinmetz Parameters

In modern power electronic systems, voltages across inductors/transformers generally show rectangular shapes, as the voltage across an inductor/transformer can be positive, negative or zero. In the stage of zero applied voltage (constant flux) core losses are not necessarily zero. At the beginning of a period of constant flux, losses still occur in the material. This is due to relaxation processes. A physical explanation about magnetic relaxation is given and a new core loss modeling approach that takes such relaxation effects into consideration is introduced. The new loss model is called i2GSE and has been verified experimentally.

https://www.hpe.ee.ethz.ch/uploads/tx_ethpublications/05955126.pdf

Improved Core-Loss Calculation for Magnetic Components Employed in Power Electronic Systems

Nonsinusoidal voltage waveforms are quite common in high frequency power conversion magnetics. Low frequency nonsinusoidal waveforms are also common in ac motor applications with waveforms such as pulsewidth modulation and six-step. Previous attempts to model these losses, based on the Steinmetz equation, can work only in a limited range of frequencies, flux density excitations, and waveforms. In this paper, we present a very practical, yet very general and accurate model, for core loss calculations in case of nonsinusoidal voltage waveforms. We show the model is equally applicable to low and high frequencies, metallic as well as nonmetallic (e.g., ferrites) core materials, by comparing the model prediction with measured data for various waveforms, frequencies, and flux densities. The model can be used for the design of high frequency transformers and inductors for use in switched mode power supplies. The model can also be used for ac motors where it is hard to estimate "derating factor" and to avoid uncontrolled temperature rise

A Practical, Accurate and Very General Core Loss Model for Nonsinusoidal Waveforms

Nonsinusoidal voltage waveforms are quite common in high frequency power conversion magnetics. Low frequency nonsinusoidal waveforms are also common in AC motor applications with waveforms such as PWM and six-step. Previous attempts to model these losses, based on Steinmetz equation, can work only in a limited range of frequencies, flux density excitations and waveforms. In this paper we present a very practical, yet very general and accurate model, for core loss calculations in case of nonsinusoidal voltage waveforms. We show the model is equally applicable to low and high frequencies, metallic as well as nonmetallic (e.g. ferrites) core materials, by comparing the model prediction with measured data for various waveforms, frequencies, and flux densities. The model can be used for the design of high frequency transformers and inductors for use in switched mode power supplies. The model can also be used for AC motors where it is hard to estimate `Derating Factor' and to avoid uncontrolled temperature rise

W.A. Roshen

Papers

A Practical, Accurate and Very General Core Loss Model for Nonsinusoidal Waveforms

A practical, accurate and very general core loss model for nonsinusoidal waveforms