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Effect of Air Gap on the Performance of Hybrid Planar Power Transformer in High Frequency (MHz) Switch Mode Power Supplies (SMPS)
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media. (Power Electronics)
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media. (Power Electronics)ORCID iD: 0000-0001-5326-2563
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media. (Power Electronics)
2012 (English)In: Proceedings of INDUCTICA 2012, Coil Winding, Insulation and Electrical Manufacturing International Conference and Exhibition (CWIEME), Berlin, Germany 26-28 June 2012, 2012Conference paper, Published paper (Refereed)
Abstract [en]

A half bridge transformer with novel winding strategy was designed and tested up to the output power level of 50W with a maximum energy efficiency of 98% in 1-6 MHz frequency region. In this paper, the effect of air gap on the performance of the designed transformer for high frequency (MHz) Switch Mode Power Supplies (SMPS) was studied and analyzed. The air gap of the transformer was varied from 0 – 2mm and the effect on self, leakage, mutual inductances, coupling coefficient and power transfer capability was recorded in 1 - 6MHz. The parameters of the transformer with different air gaps were extracted using network analyzer. The transformer was excited with sinusoidal voltages using power amplifier and the performance characteristics such as input impedance, power transfer capability and hence the energy efficiency was measured. At a particular operating frequency of 3MHz, the maximum power transferred for the given excitation voltage with 0mm air gap was found to be 22W whereas it is only 8W with the 2mm air gap . The measured energy efficiency of the transformer at 3MHz with 0mm and 2mm air gap was found to be 93% and 79% respectively. With this study, for the given power transfer application, at a particular high frequency operation of converter, an optimum air gap without sacrificing the energy efficiency and core saturation was proposed

Place, publisher, year, edition, pages
2012.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:miun:diva-16069Local ID: STCOAI: oai:DiVA.org:miun-16069DiVA, id: diva2:514871
Conference
INDUCTICA 2012, Coil Winding, Insulation and Electrical Manufacturing International Conference and Exhibition (CWIEME), Berlin, Germany 26-28 June 2012
Available from: 2012-04-11 Created: 2012-04-11 Last updated: 2016-10-20Bibliographically approved
In thesis
1. High Frequency (MHz) Planar Transformers for Next Generation Switch Mode Power Supplies
Open this publication in new window or tab >>High Frequency (MHz) Planar Transformers for Next Generation Switch Mode Power Supplies
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Increasing the power density of power electronic converters while reducing or maintaining the same cost, offers a higher potential to meet the current trend inrelation to various power electronic applications. High power density converters can be achieved by increasing the switching frequency, due to which the bulkiest parts, such as transformer, inductors and the capacitor's size in the convertercircuit can be drastically reduced. In this regard, highly integrated planar magnetics are considered as an effective approach compared to the conventional wire wound transformers in modern switch mode power supplies (SMPS). However, as the operating frequency of the transformers increase from several hundred kHz to MHz, numerous problems arise such as skin and proximity effects due to the induced eddy currents in the windings, leakage inductance and unbalanced magnetic flux distribution. In addition to this, the core losses whichare functional dependent on frequency gets elevated as the operating frequency increases. Therefore, this thesis provides an insight towards the problems related to the high frequency magnetics and proposes a solution with regards to different aspects in relation to designing high power density, energy efficient transformers.The first part of the thesis concentrates on the investigation of high power density and highly energy efficient coreless printed circuit board (PCB) step-down transformers useful for stringent height DC-DC converter applications, where the core losses are being completely eliminated. These transformers also maintain the advantages offered by existing core based transformers such as, high coupling coefficient, sufficient input impedance, high energy efficiency and wide frequencyband width with the assistance of a resonant technique. In this regard, several coreless PCB step down transformers of different turn’s ratio for power transfer applications have been designed and evaluated. The designed multilayered coreless PCB transformers for telecom and PoE applications of 8,15 and 30W show that the volume reduction of approximately 40 - 90% is possible when compared to its existing core based counterparts while maintaining the energy efficiency of the transformers in the range of 90 - 97%. The estimation of EMI emissions from the designed transformers for the given power transfer application proves that the amount of radiated EMI from a multilayered transformer is lessthan that of the two layered transformer because of the decreased radius for thesame amount of inductance.The design guidelines for the multilayered coreless PCB step-down transformer for the given power transfer application has been proposed. The designed transformer of 10mm radius has been characterized up to the power level of 50Wand possesses a record power density of 107W/cm3 with a peak energy efficiency of 96%. In addition to this, the design guidelines of the signal transformer fordriving the high side MOSFET in double ended converter topologies have been proposed. The measured power consumption of the high side gate drive circuitvitogether with the designed signal transformer is 0.37W. Both these signal andpower transformers have been successfully implemented in a resonant converter topology in the switching frequency range of 2.4 – 2.75MHz for the maximum load power of 34.5W resulting in the peak energy efficiency of converter as 86.5%.This thesis also investigates the indirect effect of the dielectric laminate on the magnetic field intensity and current density distribution in the planar power transformers with the assistance of finite element analysis (FEA). The significanceof the high frequency dielectric laminate compared to FR-4 laminate in terms of energy efficiency of planar power transformers in MHz frequency region is also explored.The investigations were also conducted on different winding strategies such as conventional solid winding and the parallel winding strategies, which play an important role in the design and development of a high frequency transformer and suggested a better choice in the case of transformers operating in the MHz frequency region.In the second part of the thesis, a novel planar power transformer with hybrid core structure has been designed and evaluated in the MHz frequency region. The design guidelines of the energy efficient high frequency planar power transformerfor the given power transfer application have been proposed. The designed corebased planar transformer has been characterized up to the power level of 50W and possess a power density of 47W/cm3 with maximum energy efficiency of 97%. This transformer has been evaluated successfully in the resonant converter topology within the switching frequency range of 3 – 4.5MHz. The peak energy efficiency ofthe converter is reported to be 92% and the converter has been tested for the maximum power level of 45W, which is suitable for consumer applications such as laptop adapters. In addition to this, a record power density transformer has been designed with a custom made pot core and has been characterized in thefrequency range of 1 - 10MHz. The power density of this custom core transformer operating at 6.78MHz frequency is 67W/cm3 and with the peak energy efficiency of 98%.In conclusion, the research in this dissertation proposed a solution for obtaining high power density converters by designing the highly integrated, high frequency(1 - 10MHz) coreless and core based planar magnetics with energy efficiencies inthe range of 92 - 97%. This solution together with the latest semiconductor GaN/SiC switching devices provides an excellent choice to meet the requirements of the next generation ultra flat low profile switch mode power supplies (SMPS).

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2013. p. 143
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 159
Keywords
Planar Magnetics, DC-DC Converters, Switch Mode Power Supplies, MHz Frequency Region
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-20270 (URN)STC (Local ID)978-91-87557-02-6 (ISBN)STC (Archive number)STC (OAI)
Public defence
2013-10-04, O102, Holmgatan 10, Sundsvall, 10:30 (English)
Opponent
Supervisors
Funder
EU, European Research CouncilVINNOVASwedish Energy Agency
Available from: 2013-11-22 Created: 2013-11-20 Last updated: 2016-10-19Bibliographically approved

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Ambatipudi, RadhikaKotte, Hari BabuBertilsson, Kent

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