Investigation on transformer design of high frequency high efficiency dc-dc converters
18 Mar 2010-pp 940-947
TL;DR: In this paper, the authors studied the high-frequency high-efficiency transformer design and proposed several novel concepts to reveal the essence of the transformer design, in order to minimize the winding loss, several winding structure are proposed and compared.
Abstract: This paper studies the high-frequency high-efficiency transformer design. Several novel concepts are proposed to reveal the essence of the transformer design. In order to minimize the winding loss, several winding structure are proposed and compared. The planar transformer winding with PCB or spiral windings are discussed. The key factors to achieve the low winding losses are presented. The transformer design of the LLC resonant converter is investigated. The impacts on integration of magnetizing inductance and leakage inductance are studied.
Citations
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TL;DR: A novel matrix transformer structure is proposed to integrate four elemental transformers into one magnetic core with simple four-layer print circuit board windings implementation and further reduced core loss by pushing switching frequency up to megahertz with GaN devices.
Abstract: Isolated high-output current DC/DC converters are critical for future data center power architecture. LLC converters with matrix transformer are suitable for these applications due to its high efficiency and high power density. Different matrix transformer structures are investigated in this paper. To improve the current design practice, a high-frequency transformer loss model is developed and a detailed design methodology is proposed. Moreover, a novel matrix transformer structure is proposed to integrate four elemental transformers into one magnetic core with simple four-layer print circuit board windings implementation and further reduced core loss. By pushing switching frequency up to megahertz with GaN devices, the proposed matrix transformer can achieve high efficiency, high power density, and automatic manufacturing for magnetic components. A 1-MHz 380 V/12 V 800-W LLC converter with GaN devices is demonstrated. The prototype achieves a peak efficiency of 97.6% and a power density of 900 W/in3.
305 citations
Cites background or methods from "Investigation on transformer design..."
...Although such a structure in [17] and [18] can help to reduce conduction loss and termination loss, it is too complex for manufacturing and mass production....
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...To reduce the primary ac winding loss, a hybrid transformer structure, including litz wires primary winding and print circuit board (PCB) secondary winding, is employed; to reduce the secondary termination loss, the SRs and output capacitors are mounted on the same PCB layer of the secondary winding [17], [18]....
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TL;DR: In this article, a high-efficiency high power density LLC resonant converter with a matrix transformer is proposed, which can help reduce leakage inductance and the ac resistance of windings so that the flux cancellation method can then be utilized to reduce core size and loss.
Abstract: In this paper, a high-efficiency high power density LLC resonant converter with a matrix transformer is proposed. A matrix transformer can help reduce leakage inductance and the ac resistance of windings so that the flux cancellation method can then be utilized to reduce core size and loss. Synchronous rectifier (SR) devices and output capacitors are integrated into the secondary windings to eliminate termination-related winding losses, via loss and reduce leakage inductance. A 1 MHz 390 V/12 V 1 kW LLC resonant converter prototype is built to verify the proposed structure. The efficiency can reach as high as 95.4%, and the power density of the power stage is around 830 W/in3.
194 citations
Cites background from "Investigation on transformer design..."
...This transformer structure is simplified by [24]....
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...cause of the skin effect very little current goes through the center of the terminals thus causing very high losses and generating hot spots [24]....
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...To eliminate the ac conduction loss among layers, one effective way is to mount MOSFET devices on the PCB board [24], [25]....
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TL;DR: In this article, a switch-controlled capacitor modulated LLC converter (SCC-LLC) is presented to solve the load sharing problem in LLC resonant converters by using phase shedding.
Abstract: The interleaving technique is necessary for LLC resonant converters to achieve high power level. The advantages include expanded power capacity, lower output ripple current, and higher light-load efficiency by using phase shedding. However, conventional frequency-controlled LLC converters will lose regulation in individual phases if all the phases are operating at the same switching frequency, causing load sharing problem. Existing load sharing solutions for interleaved LLC converters all have limitations. In this paper, a switch-controlled capacitor (SCC) modulated LLC converter (SCC-LLC) is presented to solve the load-sharing problem. With constant switching frequency, interleaving and phase shedding can be achieved. A 600-W, two-phase interleaved constant frequency SCC-LLC prototype is built to verify the feasibility and demonstrate the advantages.
162 citations
TL;DR: In this article, a detailed analysis of high-frequency leakage inductance and an accurate prediction methodology is proposed, where the highfrequency eddy current effects cause a reduction in leakage induction and the proximity effect between adjacent layers is responsible for the reduction of leakage induction.
Abstract: Frequency-dependent leakage inductance is often observed. The high-frequency eddy current effects cause a reduction in leakage inductance. The proximity effect between adjacent layers is responsible for the reduction of leakage inductance. This paper gives a detailed analysis of high-frequency leakage inductance and proposes an accurate prediction methodology. High-frequency leakage inductances in several interleaved winding configurations are also discussed. Interleaved winding configurations actually give a smaller degree of reduction of leakage induction at high frequency. Finite-element analysis simulation and measurement validate the models.
134 citations
Cites background from "Investigation on transformer design..."
...The accurate prediction of leakage inductance at high frequency is also critical for resonant converters because a well-matched resonant frequency is often required [6], [7]....
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TL;DR: In this article, the authors investigated the benefits of gallium nitride (GaN) devices in an LLC resonant converter and quantitatively evaluated GaN devices' capabilities to improve converter efficiency.
Abstract: Newly emerged gallium nitride (GaN) devices feature ultrafast switching speed and low on-state resistance that potentially provide significant improvements for power converters. This paper investigates the benefits of GaN devices in an LLC resonant converter and quantitatively evaluates GaN devices’ capabilities to improve converter efficiency. First, the relationship of device and converter design parameters to the device loss is established based on an analytical model of LLC resonant converter operating at the resonance. Due to the low effective output capacitance of GaN devices, the GaN-based design demonstrates about 50% device loss reduction compared with the Si-based design. Second, a new perspective on the extra transformer winding loss due to the asymmetrical primary-side and secondary-side current is proposed. The device and design parameters are tied to the winding loss based on the winding loss model in the finite element analysis (FEA) simulation. Compared with the Si-based design, the winding loss is reduced by 18% in the GaN-based design. Finally, in order to verify the GaN device benefits experimentally, 400- to 12-V, 300-W, 1-MHz GaN-based and Si-based LLC resonant converter prototypes are built and tested. One percent efficiency improvement, which is 24.8% loss reduction, is achieved in the GaN-based converter.
130 citations
Cites background from "Investigation on transformer design..."
...Previous studies have illustrated that the terminal loss, the fringe effect loss, and the intrinsic winding loss are the three dominant contributors to the high-frequency transformer winding loss [27], [28]....
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References
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07 Aug 2002
TL;DR: In this article, a LLC resonant converter is proposed for front end DC/DC conversion in a distributed power system, which utilizes leakage and magnetizing inductance of a transformer.
Abstract: A new LLC resonant converter is proposed for front end DC/DC conversion in a distributed power system. Three advantages are achieved with this resonant converter. First, ZVS turn on and low turn off current of MOSFETs are achieved. The switching loss is reduced so we can operate the converter at higher switching frequency. The second advantage is that with this topology, we can optimize the converter at high input voltage. Finally, with this topology, we can eliminate the secondary filter inductor, so the voltage stress on the secondary rectifier will be limited to two times the output voltage, better rectifier diodes can be used and secondary conduction loss can be reduced. The converter utilizes leakage and magnetizing inductance of a transformer. With magnetic integration concept, all the magnetic components can be built in one magnetic core. The operation and characteristic of this converter is introduced and efficiency comparison between this converter and a conventional PWM converter is given which shows a great improvement by using this topology.
941 citations
19 Mar 2006
TL;DR: In this paper, the relationship between converter efficiency and operation range with different circuit parameters has been revealed and an optimal design methodology has been developed based on the revealed relationship, and a 1MHz, 1kW LLC converter is designed to verify the proposed method.
Abstract: Although LLC resonant converter can achieve wide operation range with high efficiency, lack of design methodology makes it difficult to be implemented. In this paper, based on the theoretical analysis on the operation principles during normal condition and holdup time, the relationship between converter efficiency and operation range with different circuit parameters has be revealed. An optimal design methodology has been developed based on the revealed relationship. A 1MHz, 1kW LLC converter is designed to verify the proposed method.
638 citations
TL;DR: In this paper, a synchronous rectifier (SR) driving scheme was proposed for dc-dc resonant converters with SRs, which can achieve low stress, high efficiency, and high power density.
Abstract: This paper proposes a novel synchronous rectifier (SR) driving scheme for resonant converters. It is very suitable for high-frequency, high-efficiency, and high-power-density dc-dc resonant converters with SRs. In this paper, an LLC resonant converter with the proposed synchronous rectification is designed and analyzed. With the proposed driving scheme, the SR body diode conduction is reduced to almost zero. The driving scheme eliminates the reverse-recovery problem of SRs. Both current and voltage stresses are greatly decreased, and the conduction loss and switching loss of SRs are also reduced considerably. The experimental results show that the proposed LLC resonant converter with SRs can achieve low stress, high efficiency, and high power density.
304 citations
"Investigation on transformer design..." refers background in this paper
...Hence there is a large incentive to increase the overall efficiency and density of power delivery systems [1-16]....
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...Conventional PWM converters have to sacrifice normal operation efficiency to extend its operation range [1-8]....
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TL;DR: In this article, a three-level soft switching LLC series resonant dc/dc converter is presented, which achieves zero-voltage switching (ZVS) for each main switch without any auxiliary circuit.
Abstract: Paper presents a three-level soft switching LLC series resonant dc/dc converter. Zero-voltage switching (ZVS) is achieved for each main switch without any auxiliary circuit. Voltage stress of each main switch is half of input voltage. Zero-current-switching (ZCS) is achieved for rectifier diodes. Wide input/output range can be achieved under low frequency range because of two-stage resonance. Only one magnetic component is required in this converter. Efficiency is higher in high line input, so this converter is a preferable candidate for power products with the requirement of hold up time. For design convenience, relationship between dc gain and switching frequency, load resistance is deduced. Its open load characteristic and short load characteristic are exposed to provide theory basis for no load operation and over current protection. Design consideration of four dead times is presented to assure that voltage stress for main switches is within half of input voltage and ZVS for each main switch is achieved. Finally the principle of operation and the characteristics of the presented converter are verified on a 500V-700V input 54V/10A output experimental prototype, whose efficiency reaches 94.7% under rating condition.
288 citations
TL;DR: In this article, a graphical and numerical method of calculating and minimizing losses in windings, that generalizes previous findings, has been introduced using electromagnetic theory and MMF diagrams in both space and time.
Abstract: A graphical and numerical method of calculating and minimizing losses in windings, that generalizes previous findings, has been introduced Using electromagnetic theory and MMF diagrams in both space and time a method is proposed that provides insight into the mechanism of skin and proximity effect losses and that also yields quantitative results Using this method, several winding geometries for various topologies are covered The analysis and optimization process is experimentally verified using an interleaved flyback transformer The mathematical treatment justifying the use of the field method and which is essential in arriving at any numerical result is presented are more general equations for the calculation of copper losses are derived The relation between the fields in the transformer and copper losses is emphasized Also, the tools necessary to derive optimization diagrams are provided >
233 citations
"Investigation on transformer design..." refers background in this paper
...Hence there is a large incentive to increase the overall efficiency and density of power delivery systems [1-16]....
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