| 1. |
- Kotte, Hari Babu, 1979-
(författare)
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High Frequency (MHz) Resonant Converters using GaN HEMTs and Novel Planar Transformer Technology
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increased power consumption and power density demands of moderntechnologies have increased the technical requirements of DC/DC and AC/DC powersupplies. In this regard, the primary objective of the power supply researcher/engineeris to build energy efficient, high power density converters by reducing the losses andincreasing the switching frequency of converters respectively. Operating the convertercircuits at higher switching frequencies reduces the size of the passive componentssuch as transformers, inductors, and capacitors, which results in a compact size,weight, and increased power density of the converter. Therefore, the thesis work isfocussed on the design, analysis and evaluation of isolated converters operating in the1 - 5MHz frequency region with the assistance of the latest semi conductor devices,both coreless and core based planar power transformers designed in Mid SwedenUniversity and which are suitable for consumer applications of varying power levelsranging from 1 – 60W.In high frequency converter circuits, since the MOSFET gate driver plays a prominentrole, different commercially available MOSFET gate drivers were evaluated in thefrequency range of 1 - 5MHz in terms of gate drive power consumption, rise/fall timesand electromagnetic interference (EMI) and a suitable driver was proposed.Initially, the research was focused on the design and evaluation of a quasi resonantflyback converter using a multilayered coreless PCB step down transformer in thefrequency range of 2.7 – 4MHz up to the power level of 10W. The energy efficiency ofthis converter is found to be 72 - 84% under zero voltage switching conditions (ZVS).In order to further improve the energy efficiency of the converter in the MHzfrequency region, the new material device GaN HEMT was considered. Thecomparisons were made on a quasi resonant flyback DC-DC converter using both theSi and GaN technology and it was found that an energy efficiency improvement of 8 –10% was obtained with the GaN device in the frequency range of 3.2 – 5MHz. In orderto minimize the gate drive power consumption, switching losses and to increase thefrequency of the converter in some applications such as laptop adapters, set top box(STB) etc., a cascode flyback converter using a low voltage GaN HEMT and a highvoltage Si MOSFET was designed and evaluated using a multi-layered coreless PCBtransformer in the MHz frequency region. Both the simulation and experimentalresults have shown that, with the assistance of the cascode flyback converter, theswitching speeds of the converter can be increased with the benefit of obtaining asignificant improvement in the energy efficiency as compared to that for the singleswitch flyback converter.In order to further maximize the utilization of the transformer, to reduce the voltagestress on MOSFETs and to obtain the maximum power density from the convertercircuit, double ended topologies were considered. Due to the lack of high voltage highside gate drivers in the MHz frequency region, a gate drive circuitry utilizing themulti-layered coreless PCB signal transformer was designed and evaluated in both ahalf-bridge and series resonant converter (SRC). It was found that the gate drive powerconsumption using this transformer was around 0.66W for the frequency range of 1.5 -v3.75 MHz. In addition, by using this gate drive circuitry, the maximum energyefficiency of the SRC using multilayered coreless PCB power transformer was found tobe 86.5% with an output power of 36.5W in the switching frequency range of 2 –3MHz.In order to further enhance the energy efficiency of the converter to more than 90%,investigations were carried out by using the multiresonant converter topology (LCCand LLC), novel hybrid core high frequency planar power transformer and the GaNHEMTs. The simulated and experimental results of the designed LCC resonantconverter show that it is feasible to obtain higher energy efficiency isolated DC/DCconverters in the MHz frequency region. The peak energy efficiency of the LCCconverter at 3.5MHz is reported to be 92% using synchronous rectification. Differentmodulation techniques were implemented to regulate the converter for both line andload variations using a digital controller.In order to realize an AC/DC converter suitable for a laptop adapter application,consideration was given to the low line of the universal input voltage range due to theGaN switch limitation. The energy efficiency of the regulated converter operating inthe frequency range of 2.8 – 3.5MHz is reported to be more than 90% with a loadpower of 45W and an output voltage of 22Vdc. In order to determine an efficient powerprocessing method on the secondary side of the converter, a comparison was madebetween diode rectification and synchronous rectification and optimal rectification wasproposed for the converters operating in the MHz frequency range for a given powertransfer application. In order to maintain high energy efficiency for a wide load rangeand to maintain the narrow switching frequency range for the given input voltagespecifications, the LLC resonant converter has been designed and evaluated for theadapter application. From the observed results, the energy efficiency of the LLCresonant converter is maintained at a high level for a wide load range as compared tothat for the LCC resonant converter.Investigations were also carried out on isolated class E resonant DC-DC converter withthe assistance of GaN HEMT and a high performance planar power transformer at theswitching frequency of 5MHz. The simulated energy efficiency of the converter for theoutput power level of 16W is obtained as 88.5% which makes it feasible to utilize thedesigned isolated converter for various applications that require light weight and lowprofile converters.In conclusion, the research in this dissertation has addressed various issues related tohigh frequency isolated converters and has proposed solution by designing highlyenergy efficient converters to meet the current industrial trends by using coreless andcore based planar transformer technologies along with the assistance of GaN HEMTs.With the provided solution, in the near future, it is feasible to realize low profile, highpower density DC/DC and AC/DC converters operating in MHz frequency regionsuitable for various applications.
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| 2. |
- Ambatipudi, Radhika, 1982-
(författare)
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High Frequency (MHz) Planar Transformers for Next Generation Switch Mode Power Supplies
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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).
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| 3. |
- Bakar, Muhammad Abu, 1969-
(författare)
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Wide Range Isolated Power Converters
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Power electronics technology is rapidly growing in most industrialapplications. There is an increasing demand for efficient and low profilepower converters in the industry like automotive, power grids, renewableenergy systems, electric rail systems, home appliances, and informationtechnology. In some applications, there is an increasing demand for powerconverters showing a stable performance over a wide variation in inputvoltage, whereas in others the demand is for converters showing a stableperformance over a wide variation of output voltage. In this regard, not somuch work has been done to combine both requirements into one solution;this is the primary focus of the dissertation. It presents a unique solution tothe industry, which addresses both requirements. The technique can beapplied in a one size fits all solution which not only extends the range of theline voltage and the output voltage but also provides the flexibility to adjustthe required set of line/output voltage. The variation in line voltage severelydegrades the performance of power converters because of the extendedfreewheeling interval, more circulating current, narrow range of zero voltageswitching and increased EMI. To overcome this, the converter consists of tworeconfigurable modes on the input side that can be configured following thevariation in line voltage to maintain a stable performance. In addition, itproposes three reconfigurable steps for the output voltage, which can be usedto adjust the output voltage from base level X to 2X and 4X in discrete stepsand/or from X - 4X volt while showing stable performance. This makes theproposal a 2x3 reconfigurable modes power converter, which means that thegain of the proposed converter can be raised to 4 or 8. Furthermore, theflexibility in the reconfigurable structure simplifies the implementation of theproposed single solution in a range of applications. Each concept proposed inthe thesis is verified analytically, experimentally and modelling it into aSPICE simulation. Then the whole concept is confined into a single entity,which is applied in an example application of a phase shifted full bridgeconverter. The full converter is characterized for input voltage 100-400Vdc, theoutput voltage 24-96Vdc, and up to the load power of 1kW.
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