Planar Magnetics Research Articles

Thermal Resistance Modeling for the Optimal Design of EE and E/PLT Core-Based Planar Magnetics

With the integration of power electronic converters and components, an accurate thermal design becomes essential. Hence, precise thermal models for components are needed for their optimal design. This paper focuses on the development of an analytical model for the design of thermal resistance of planar magnetic cores (PMC). Based on computational fluid dynamic (CFD) simulations, the PMC design thermal resistance variation is studied, according to ambient temperature and level of losses. Then, a polynomial equation is developed to model those variations, and coefficients are deduced for all the sizes of PMC. This analytical model, useful for designers, is finally validated with thermal measurements on a planar transformer prototype.

A Comprehensive Review on Planar Magnetics and the Structures to Reduce the Parasitic Elements and Improve Efficiency

Due to the need for highly efficient and compact power electronic converters to operate at higher frequencies, traditional wire-wound magnetics are not suitable. This paper provides a comprehensive review of planar magnetic technologies, discussing their advantages as well as associated disadvantages. An extensive review of the research literature is presented with the aim of suggesting models for planar magnetics. Several strategies are proposed to overcome the limitations of planar magnetics, including winding conduction loss, leakage inductance, and winding capacitance. The goal of this study is to provide engineers and researchers with a clear roadmap for designing planar magnetic devices.

Development of Phase-Shift Full-Bridge Converter With Integrated Winding Planar Two-Transformer for LDC

This study proposes a new phase-shift full-bridge (PSFB) converter with an integrated winding planar two-transformer for a low-voltage dc–dc converter (LDC). An LDC is a dc–dc converter that supplies power to a 12-V auxiliary battery (A_BAT) and loads from the main battery (M_BAT) of electric vehicles (EVs), used in low-voltage and high-current output applications. PSFB converter is widely used as a suitable topology for such systems. In order to improve the power density, the integrated planar magnetics is designed in the proposed PSFB converter. Furthermore, the size of the transformer is optimized considering the footprint and core loss of components. To confirm the validity of the proposed converter, a 2.1-kW prototype LDC with an input voltage range of 400–800 V and an output voltage of 14 V is analyzed, and the operating characteristics are described. The proposed converter achieves a maximum efficiency of 95.4% and a power density of 5.2 kW/L.

High Performance Planar Magnetics Based on an Unbalanced-Flux Approach

This paper presents a new design concept to increase the efficiency and the power density of planar magnetics. In contrast to the existing magnetics, which are built using the balanced magnetic flux density design, the proposed design concept generates unbalanced magnetic flux density across the different parts of the magnetic core. The theoretical analysis shows that the core loss of the unbalanced-flux design can be reduced by more than 50% compared to the existing one. The core loss reduction brings several benefits to planar magnetics such as: high power capability, better thermal performance and wider safe operating area (SOA). The proposed design is experimentally evaluated and compared with the balanced-flux design. The experimental results are in good consistency with its theoretical counterparts. The measured core loss are decreased by more than 50% and the power density is increased by more than 250%.

Thermal Modeling of Planar Magnetics: Fundamentals, Review and Key Points

High-frequency and high-power density converters are essential for many applications such as automotive and more electric aircraft. To improve power density, planar magnetic components are increasingly used in power electronic converters owing to their advantages, such as less high-frequency losses, repeatability, and better thermal performance compared to conventional wound components. Considerable attention has been paid to their electrical performance. However, the thermal aspects are essential for enhancing completely their performance. Currently, there is an increasing interest in these critical aspects of high-density power converters. This paper presents a literature review of studies on the thermal modeling of planar magnetics. The papers were organized according to the model type and analyzed to highlight their merits and limitations. A multicriteria comparison of the studied papers was performed. Moreover, the key points and issues related to the thermal modeling are addressed to guide designers in enhancing the thermal aspects of planar magnetic components.

Overview of Planar Magnetics for High-frequency Resonant Converters

Overview of Planar Magnetics for High-frequency Resonant Converters

Variable-Switching-Frequency Single-Stage Bidirectional GaN AC–DC Converter for the Grid-Tied Battery Energy Storage System

This article presents a 10-kW novel gallium-nitride (GaN)-based three-phase grid to 48-V battery energy storage system (BESS). The BESS utilizes a single-stage ac–dc dual-active-bridge (DAB) converter with dual-phase-shift (DPS) and variable-frequency (VF) control. 600- and 80-V GaN power transistors, as well as planar magnetics, are used to achieve 96.6% efficiency and 50-W/in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^3$</tex-math></inline-formula> power density. The operation principle and power transfer characteristics are derived based on time-domain analysis of the DAB inductor current. VF and DPS are utilized to achieve power factor correction and zero-voltage switching simultaneously while minimizing the DAB rms current. An online calculation algorithm is presented with short execution time, which enables the closed-loop control of the BESS. Experimental results are presented to validate the novel control.

Planar Magnetic Integration Design Based on LLC Resonant Converter

High power density and high efficiency is a major trend in the development of power converters. The main measure to reduce the size of power converter is to improve the working frequency, and the limiting factor is the size of magnetic components. With the development of new semiconductor devices, the working frequency of power converters has been significantly improved, which gives us the opportunity to apply printed circuit board (PCB) winding planar magnetics. Compared with the traditional high frequency magnetics, planar magnetics not only reduce the size of the magnetic components effectively but also improve reliability through repeatable automated manufacturing, which is convenient for large-scale production. Magnetic integration is another method to reduce the size of the power converter. In this paper, a new magnetic structure based on PCB winding is proposed, which integrates inductance and transformer into one component. And the inductor can be independent of the transformer. In this structure, the inductance of inductor and excitation inductance of transformer can be easily controlled by changing the number of winding turns or the length of the air gap. A 20-W 200-kHz half-bridge LLC resonant converter with a peak efficiency of 94.9% is built to verify the feasibility of the designed planar magnetic integrated structure.

A Novel High-Current Planar Inductor With Cooling Fins Based on 3-D Printing

This letter proposed a novel high-current planar inductor with cooling fins based on 3-D printing and its copper winding is 3-D printed by using selective laser melting technology. The 3-D-printed winding is designed for high-current applications based on 3-D space and can work as both winding and cooling fins. Compared with conventional printed circuit board (PCB) planar inductor, the proposed planar inductor not only has better performance, such as low dc resistance (DCR), ac resistance, and temperature rise, without volume increasing, but also has the superiorities of conventional PCB planar magnetics, such as ease of manufacture and controllability. To verify its performance, a 100-A-output buck converter using the proposed inductor was fabricated and compared with another identical buck converter using a conventional PCB inductor with the same size. The DCR of the proposed inductor is almost one-fifth of the PCB inductor. Besides, the efficiency of the buck converter with the proposed inductor is always over 0.5% higher than that with PCB inductor under different loads and its maximum efficiency is nearly 1% higher at light load. Furthermore, the maximum temperature rise of the proposed inductor is 26.8 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C under full load, only one-third of the PCB planar inductor. In other words, the proposed inductor can work well under 100-A current, whereas the traditional PCB inductor cannot due to too high temperature (103.8 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C).

Review design of E-Motorcycle charger topology for DC house using planar magnetics

Following the global trend of adopting renewable energy into the electric power system, many direct currents (DC) houses concepts are proposed. Most of the renewable energy systems are based on DC voltage sources. This paper discussed the development of a lightweight, low-profile, and built-in electric motorcycle (E-Motorcycle) charger that does not take excessive space and compatible with the DC house system. A topology comparison in high switching frequency above 1 MHz using planar magnetics is performed to select the most suitable DC-DC converter. A wide bandgap (WBG) devices are used to achieve high efficiency in high switching frequency and reduce the charger’s size. Simulation results and design of the selected topology is presented.

Power Density Optimization of 700 kHz GaN-Based Auxiliary Power Module for Electric Vehicles

This article proposes a high-power density 1.8 kW auxiliary power module (APM) for electric vehicles (EVs) based on gallium nitride devices. A design procedure for the high-frequency phase-shift full-bridge with current-doubler rectifier using printed circuit board (PCB)-based planar magnetics is proposed. Leakage inductance analysis of the high-frequency pulsewidth-modulation converter is given to achieve both regulation and zero-voltage-switching turn- on . Then, the magnetics optimization procedure for the customized planar core is proposed with a magnetic figure-of-merit concept to meet the high-power density target. Technical considerations are detailed to meet the extreme temperature constraint imposed on the EVs components. Finally, the proposed APM is demonstrated with a switching frequency of 700 kHz and a power density of 8.1 kW/L (132.8 W/in3).

High-Frequency PCB Winding Transformer With Integrated Inductors for a Bi-Directional Resonant Converter

The momentum toward high power density high-efficiency power converters continues unabated. The key to reducing the size of power converters is high-frequency operation and the bottleneck is the magnetic components. With the emerging widebandgap devices, the switching frequency of power converters increases significantly, to hundreds of kilohertz, which provides us the opportunity to adopt printed circuit board (PCB) winding planar magnetics. Compared with the conventional litz-wire-based magnetics, planar magnetics can not only effectively reduce the converter size, but also offer improved reliability through automated manufacturing process with repeatable parasitics. Another way to reduce the number of magnetic components and shrink the size of power converters is through the magnetic integration. In this paper, a novel PCB winding based magnetic structure is proposed to integrate both inductor and transformer into one component. In this structure, the inductor value can be easily controlled by changing the cross-sectional area of the core or the length of the air gap. A 6.6-kW 500-kHz CLLC resonant converter prototype with 98% efficiency and 130-W/in3 (8 kW/L) power density is built to verify the feasibility of the proposed PCB winding based magnetic structure.

High-Frequency Three-Phase Interleaved LLC Resonant Converter With GaN Devices and Integrated Planar Magnetics

The LLC converter is deemed the most widely used topology as dc/dc converter in server and telecom applications. To increase the output power and reduce the input and output current ripples, three-phase interleaved LLC converter is becoming more and more popular. It has been demonstrated that three interleaved LLC converter can achieve further efficiency improvement at the 3-kW power level. However, the magnetic components for multiphase LLC converter are complex, bulky, and difficult to manufacture in a cost-effective manner. In this paper, a high-frequency gallium nitride (GaN)-based three-phase LLC converter is employed to address these aforementioned challenges. With GaN operating at 1 MHz, all magnetic components, namely, three inductors and three transformers, can be integrated into one common structure while all magnetic windings implemented in a compact four-layer PCB with 3-oz copper. The proposed structure can be easily manufactured cost-effectively in high quality. Furthermore, shielding techniques for full-bridge secondary have been investigated, and additional two-layer shielding has been integrated to reduce common-mode noise. A 1-MHz 3-kW 400 V/48 V three-phase LLC converter is demonstrated, and the peak efficiency of 97.7% and power density of 600 W/in3 (37 kW/L) are achieved.

Three-Dimensional Frequency-Dependent Thermal Model for Planar Transformers in LLC Resonant Converters

In this paper, a thorough thermal analysis is carried out in order to find an analytical three-dimensional (3-D) frequency-dependent thermal model of planar transformers (PTs) used in high-frequency power converters. Because of the tendency of having higher power density as well as miniaturization of power converters, the components have to work near their thermal limit margins. This issue is more critical for planar magnetics in LLC converters due to their variable high-frequency operation, making thermal modeling and heat transfer analysis tools necessary. The proposed 3-D frequency thermal model is obtained based on the lumped parameters network (LPN) according to different thermal resistances of the PT including convection, conduction, and radiation heat exchanges. It should be noted that not only the 3-D geometry effect of the core is applied to the proposed model, but thermal surface resistances are also considered to model the high-frequency operation effect. Moreover, the lumped capacitance thermal model is used to analyze the transient thermal variation of the transformer. The LLC resonant converter with two PTs, including EE58/11/38 and ER51/10/38 planar cores, is considered to show the compatibility of the proposed 3-D-frequency LPN model. In addition, the temperature distribution of different parts of the transformers is evaluated using finite element method modeling and compared with the proposed 3-D frequency-dependent LPN model. Experimental results confirm the improved accuracy of the proposed LPN model and show the proposed model predicts the temperature distribution in PTs with an error of less than 3%. Considering the improved accuracy and low computational time of the method, the proposed 3-D frequency-dependent model is a powerful and fast design tool to evaluate the temperature distribution for different designs, and so can be used to effectively optimize the transformer from thermal point of view.

Analysis and Design of a 1-MHz Bidirectional Multi-CLLC Resonant DC–DC Converter With GaN Devices

A 1-MHz half-bridge high-gain multi- CLLC bidirectional resonant converter with (gallium nitride) GaN field effect transistor (FETs) and integrated planar magnetics is proposed in this paper. It presents excellent gain characteristic and high power density, which is very suitable for a distributed energy storage system. The operation principle, topology features, and parameter design method of the converter are discussed in detail. The improved winding method of integrated planar magnetics is also elaborated. And then, a 400-W prototype is established and the corresponding experiments are carried out in 1 MHz. Finally, the accuracy and correctness of the theory are verified and the highest efficiency of the converter can reach 94.3%.

Analysis and Design of a 1-MHz Single-Switch DC–DC Converter With Small Winding Resistance

A 1-MHz single-switch dc–dc converter, which has a good step-up ability, is proposed in this paper. Under a high-frequency condition, the volume of passive components can be greatly reduced, and the power density can be significantly improved. The operating principles of the proposed converter are analyzed, and its system performance, including the parasitic components, is mathematically derived. To improve the boost ability and efficiency of the converter, planar magnetics with a nonuniform width winding structure are adopted in the converter, which can achieve smaller parasitic resistance. A prototype is built to verify the feasibility of the proposed high-frequency converter.

A High-Frequency CLCL Converter Based on Leakage Inductance and Variable Width Winding Planar Magnetics

A CLCL resonant DC/DC converter based on the transformer leakage inductance is proposed in this paper. With the adoption of leakage inductance, the system volume and magnetic losses can be greatly reduced. The optimal design method of the proposed converter is analyzed in detail. Also, the advantages of the CLCL converter are depicted compared with LLC circuit. The design of variable width winding planar magnetics is depicted in detail, which can reduce the winding losses and parasitic capacitance. A 1-MHz prototype using gallium nitride FETs is built to verify the feasibility of the proposed resonant converter and design method.

A 1 MHz Half-Bridge Resonant DC/DC Converter Based on GaN FETs and Planar Magnetics

A 1 MHz half-bridge resonant dc/dc converter based on GaN FETs and planar magnetics is proposed in this paper, which improves the system efficiency and power density. The resonant network can achieve satisfactory soft-switching characteristics based on a small impedance angle, which greatly reduces the losses of switches and diodes. The losses characteristics during the turn-on and turn-off transitions are analyzed in detail. The calculation results show that the GaN FETs with low output capacitance and on resistance can achieve fast switching speed and low losses in high-frequency conditions. To reduce the profile and increase the power density of the system, planar magnetics are used in this paper. The response surface methodology (RSM) and modular layer model (MLM) are adopted to help design the planar inductor and transformer, respectively. Both of the methods offer clearer and more effective ways to design the planar magnetics. A 25-W prototype is built to verify the feasibility of the proposed high-frequency converter.

Planar Magnetics for Optimised Manufacturing, Performance and Limitations

The LION Navigator, as a standard product line of Airbus Defence and Space, has started a design for manufacturing initiative for switched mode power supplies in the year 2010.An analysis of the overall production effort of power supplies reveals that a high proportion is related to hand soldering of through-hole parts, integration of the PCB into the frame and conventional magnetics which are manufactured with low automatization. A concept study was originated to evaluate the technical prospects for an improved design for manufacturing strategy.The technical approach is related to substitution of remaining through-hole parts by SMD devices if it is economic, to cool Power-SMDs via PCB to structure and, last but not least, to replace conventional magnetics with planar ones, as main part of the study. The windings of planar magnetics are integrated into the PCB with a highly automated process. They provide advantages due to good cooling capability and a low component height but advanced calculation methods are necessary to succeed in the design. As a follow up to the study the development of the power converter for the LION Navigator was started in order to detail the hardware related to an improved design for manufacturing.

Implementation of a Nonlinear Planar Magnetics Model

A nonlinear lumped element model for planar magnetics is presented. This technique develops an equivalent circuit model for multilayer planar magnetic components using 1-D analysis of Maxwell's equations. Conducting layers are represented as impedance networks, while the insulating regions are modeled as air-cored inductors. The equivalent circuit model is extended by representing the nonlinear magnetic core material as a nonlinear impedance whose magnetization characteristic is based on the Jiles–Atherton hysteresis model as well as modeling skin and proximity effects in the conductors and current distribution across windings, the improved model also integrates hysteresis loss of the magnetic core and saturation effects. The technique can be implemented in circuit simulation software. A prototype planar transformer, using printed circuit boards to mount windings, was characterized to validate the performance of the model. It is demonstrated that the developed nonlinear model more accurately represents the characteristics of the experimental transformer compared to the existing linear lumped element model. This includes the effect of core saturation on the input current and output-voltage waveforms. The technique is generalized and can be applied to many topologies and geometries.