Printed Circuit Board Winding Research Articles

Circulating and Eddy Current Losses in Coreless Axial Flux PM Machine Stators With PCB Windings

Printed circuit board (PCB) stators in coreless axial flux permanent magnet (AFPM) machines have been proposed, designed, and studied for use in multiple industries due to their design flexibility and reduction of manufacturing costs, volume, and weight compared to conventional stators. This paper investigates mechanisms and methods of approximating open circuit losses in PCB stators within example wave and spiral winding topologies for a dual rotor, single stator configuration using 3D FEA, analytical hybrid techniques and experiments. The effect of rotor magnet shape, end winding, and active conductor geometry on eddy currents is studied, and some mitigation techniques are proposed. Through stator equivalent circuit analysis, circulating current losses caused by mechanical abnormalities and magnetic circuit asymmetry are assessed. Possible strategies and schemes to minimize circulating current losses are also described. The trade-off between stator loss components and some practical design considerations are outlined in detail. The open circuit power losses of a prototype coreless AFPM motor were experimentally tested using multiple example PCB stators and emulated rotor asymmetries, with the findings being comparable to the FEA and hybrid analytical methods results.

LLC 공진형 컨버터를 위한 인덕터 집적 평면형 변압기의 설계 및 구현

The miniaturization of magnetic components is one of the most important issues in the design and fabrication of high-density switching power converters. In recent years, an integrated magnetics (IM) technique has been considered a possible solution for reducing the size and cost of the magnetic components. This paper deals with the design and implementation of an inductor integrated planar transformer for improving the power density of an LLC esonant converter. The proposed technique utilizes a leakage layer inserted between the primary and secondary printed circuit board (PCB) windings to implement a series resonant inductor in the transformer without any additional windings. The analysis and design method of the proposed inductor integrated transformer are discussed, and the implementation of the transformer using the PCB windings and magnetic sheets is presented. The implemented inductor integrated transformer is applied to the actual LLC resonant converter with a power rating of 750 W. The experiments are carried out for the actual converter, and the effectiveness of the proposed technique is verified from the experimental results.

Design and Optimization of an Integrated Resonant Inductor With High-Frequency Transformer for Wide Gain Range DC–DC Resonant Converters in Electric Vehicle Charging Applications

Large-scale adoption of wide band gap semiconductors in switched mode power converters enables miniaturization of power electronic systems. With switching frequencies approaching a few hundred kilohertz - megahertz range, efficient and compact design of magnetic components are crucial for future generation power supplies in data centers or electric vehicle (EV) applications. In a typical two-stage AC-DC power supply, the DC-DC stage is often constructed using a resonant converter with galvanic isolation provided by a high-frequency transformer. In such systems, the integration of an inductor in the resonant network with the transformer helps improve power density and reduces component count and cost. However, the integration of magnetic components can result in increased losses, deteriorating the performance of the power conversion system. In this paper, a magnetic structure along with an optimization methodology is presented to integrate a predefined resonant inductor as leakage inductance of the high-frequency transformer achieving minimum penalty on converter efficiency using planar core geometry and printed circuit board (PCB) based windings. The proposed methodology is applied to integrate a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$7.8 \mu \rm{H}$</tex-math></inline-formula> inductor with a 2:1 transformer for a 6.6 kW, 500 kHz LCL-T resonant DC-DC stage utilizing GaN transistors in an onboard battery charging converter. On the prototype converter using the optimized integrated magnetic component, a peak efficiency of 98.4% was obtained using PCB windings. Furthermore, the integrated magnetic component achieved 64 kW/L power density in the demonstrator prototype.

Compact Integrated Transformer – Grid Inductor Structure for E-Capless Single-Stage EV Charger

This article proposes a planar magnetic integration technique that combines the grid inductors and transformer in the single-stage E-capless electric vehicle charger into one core. The proposed integration technique reduces the number of magnetic components; therefore, the cost, total magnetic core loss, and volume can be significantly reduced. Using the integrated structure, the overall converter power density increases up to 11.1% compared to the nonintegrated one. This article also presents a detailed analysis of the optimal printed circuit board (PCB) winding arrangement considering both ac resistance and winding stray capacitance. Due to the high dc resistance of PCB winding, Litz wire was also considered for the proposed integrated structure. The effectiveness of the proposed structure was validated by implementing it on a 3.7-kW prototype of a single-stage ac–dc converter. Results show that the prototype with the proposed integrated structure achieved higher efficiency with both PCB winding and Litz wire. Peak efficiency of 97.17% and 6.55-kW/L power density were achieved.

Low-Loss Segmented Shielding Technique for PCB-Winding Planar Transformers

Printed-circuit-board (PCB) winding planar transformers have been widely adopted in isolated high-efficiency and high-power-density converters. Inserting the shielding layer is an effective method to attenuate the common-mode noise induced by the large interwinding capacitance of PCB winding. This letter identifies that a part of the magnetic flux will pass through the shielding layer due to the planarized structure of the planar transformer. Furthermore, the generation mechanism and the distribution of eddy current and related loss in the shielding layer are revealed. In order to reduce the eddy current loss in the shielding layer, a segmented shielding technique is proposed. The shielding layer is divided into multiple segments to reduce the coupled flux and the eddy current loss in each segment of the shielding layer. The experimental results on a 300 kHz 1000 W/28 V output resonant converter validate that, compared with the conventional shielding method, the proposed shielding technique can improve the efficiency by 0.15% at full load.

A Novel Pyramid Winding for PCB Planar Inductors With Fewer Copper Layers and Lower AC Copper Loss

Relying on the advantages of small size, good controllability, and consistency, printed circuit board (PCB) inductors are being widely used. For PCB inductors, reducing copper loss is one of the key issues. Although some research works focus on fringing effect in PCB planar winding, there are few methods to reduce proximity loss for PCB inductor. Regarding the abovementioned issues, this letter first improves the Ferreira’s 1-D copper loss model to accommodate the core feature of PCB winding: variable number of turns per layer. With this model, pyramid theorem is proposed that putting the layer with fewer turns into positions farther away from the air gaps can lower the total winding loss. Based on the theorem, this letter proposes a novel PCB inductor-winding structure named pyramid winding, which has fewer (or equal) turns on layers farther from air gaps. Pyramid winding has less copper loss, fewer copper layers, smaller size, and lower cost. In the experiment, inductor prototypes with the same six turns and ferrite pot cores but different PCB winding arrangements are built for a 300-kHz 2700-W LLC converter. Tests on inductor resistance and converter efficiency are done, and the pyramid theorem and the effectiveness of pyramid winding are verified.

Planar Common-Mode EMI Filter Design and Optimization for High-Altitude 100-kW SiC Inverter/Rectifier System

Silicon-carbide (SiC) devices are receiving popularity for high-power converter systems in aircraft due to many advantages over silicon counterparts. However, the electromagnetic interference (EMI) problems are more serious with the SiC devices operating at higher switching speeds and higher switching frequencies. The common-mode (CM) EMI filter design of the high-power SiC converter is especially challenging for high-altitude applications due to the harsher requirements of insulation and heat dissipation. The optimization of the parameters and physical design of a CM EMI filter in a 100-kW SiC inverter/rectifier system operating at 50 000 ft is conducted in this article to obtain the highest power density. The effect of the switching frequency on the EMI filter volume and the total power density of the converter system is analyzed. The lower breakdown voltage of air and the higher thermal resistance of natural convection make the conventional design of the CM choke infeasible at high altitudes. A printed circuit board (PCB)-based planar CM choke is designed with the consideration of partial discharge (PD) and heat dissipation at the altitude of 50 000 ft. The structure of the CM choke is optimized with embedded electric-field shielding plates, which controls the electric-field intensity in the air below 300 V/mm. The PCB windings improve the efficiency of heat dissipation at high altitudes and reduce the profile of the CM choke. A Pareto optimization is conducted to minimize the size of the choke and the volume of the final design is only 155 cm3. The experimental results show that the CM noise is reduced effectively with the CM EMI filter. PD is not observed even at the altitude of 50 000 ft and the thermal performance is excellent with a current of 190 A. With the optimization and the dedicated design of the CM EMI filter, the power density of the converter system is up to 33.3 kW/L.

Impact of Slit Configuration on Eddy Current and Supply Current Losses in PCB Winding of Slotless PM Machines

Applied to the production of windings, the printed circuit board (PCB) technology is promising for developing high performance slotless permanent magnet machines, since it allows for winding shapes and topologies that are difficult to obtain with the classical wire technology. However, compared with wire windings, PCB windings are more prone to eddy current losses because of the high width-to-thickness ratio of the conductor cross-section. To counteract these eddy currents, the conventional solution consists of reducing the width of the conductive tracks constituting the winding in conjunction with an increased number of turns. To keep the supply voltage within limits compatible with the power supply, parallel connections of the tracks at the winding terminals are required. This article tackles the eddy current problem differently by adding some slits distributed along the conductive tracks. This amounts to carry out local parallelizations without impacting the motor supply voltage. By means of parametric analyses carried out on different slit configurations and considering their impact on both the supply and eddy current losses, this study shows that a parallel reconnection of successive tracks two by two gives almost the same results as a classical parallel connection of all the tracks, independently of the winding shape. Furthermore, this article concludes that the optimal number of parallel slits is fixed and valid for a large range of nominal speed-torque ratios. However, it is necessary to increase the width of the slits when this ratio becomes very high and it is technically no longer possible to increase the number of slits.

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.

Thermal Design, Optimization, and Packaging of Planar Magnetic Components

This article is focused on the thermal design and three-dimensional (3-D) package optimization of planar magnetic components (PMCs), including transformers and inductors for application in an electric vehicle composite boost dc-dc converter. Each PMC comprises electrical windings in printed circuit board (PCB) form in combination with a ferrite core. Multiple features of each PMC package are thermally optimized for the proposed device configurations with given core size, core loss distribution, number of turns in the PCB winding, winding copper thickness, and winding loss distribution. These heuristically optimized features include a lower level cold plate structure with a conformal base for enhanced convective heat transfer, an upper level PMC cap structure for doubled-sided cooling through conductive heat flow to the cold plate, the implementation of functionally distributed copper thermal and electrothermal vias in the PCB winding for improved cross-plane thermal conductance, and judicious implementation of select materials at various locations and interfaces within the package. Detailed numerical modeling reveals the combined effect of this 3-D packaging strategy with a 79.3 °C and 48.5 °C maximum temperature reduction in the core and PCB winding, respectively, relative to a baseline device configuration. Select PMC experimental validation confirms the expected thermal performance of an optimized PCB design. The thermal design approach is relevant for a range of high-power-density electronics PMC packaging applications.

High-Voltage Insulation Design of Coreless, Planar PCB Transformers for Multi-MHz Power Supplies

This article investigates the insulation design for printed, planar, coreless, and high-frequency transformers with high isolation-voltage. By using finite element analysis on 2-D axial-symmetry, the transformer circuit parameters and electric field distribution are modeled and estimated. Several transformers are designed for an operating frequency of 6.78 MHz. The high frequency, coreless design allows for using thicker insulation material while ensuring a high transformer efficiency. The inclusion of the coupling capacitance in the design optimization results in several design solutions with the same figure of merit, but with different footprint and isolation voltages. Moreover, high electric fields are identified around the sharp edges of the printed circuit board (PCB) windings. Finally, the electrical and isolation performance is verified experimentally. The measured electrical properties are close to the simulated values, validating the chosen model. Breakdown tests demonstrate the feasibility of isolation voltage levels up to several tens of kilovolts. The majority of breakdowns occurs at the outer edge of the PCB winding that was identified as a high-field area. Additionally, a concept for grading the electric field of PCB windings is also proposed. Based on the results, the design aspects are discussed in detail for planar, high-frequency isolation transformers with medium-voltage isolation level.

Comparison of PCB winding topologies for axial‐flux permanent magnet synchronous machines

Although axial-flux permanent magnet machines have high torque densities, challenges regarding mass production of stators make them a less appealing choice. Printed circuit board (PCB) axial-flux machine is a type of machine with a stator that is made of layers of PCB. Given the precise, fast, and cheap mass production capabilities of PCB manufacturers, PCB axial-flux machines stand as a viable alternative for conventional round-wire winding machines. In this study, five different winding topologies are compared. Their induced phase voltages and torque are calculated using the developed magnetic scalar potential method and finite element analysis (FEA). Proposed windings are tested on a 16-pole, 2000-RPM, double rotor-single stator axial-flux permanent magnet synchronous machine. Results showed that the parallel winding had the smallest resistance and loss. Moreover, radial and concentric winding had the highest induced voltage and torque while the radial winding had 20% less phase resistance than concentric. Also, the induced voltage of radial winding had the smallest total harmonic distortion in comparison with other winding types. A novel unequal width parallel winding is proposed and it is compared with parallel winding separately. It is found that by simply increasing the cross-section area of wave windings, it is possible to decrease copper loss by 17%.

Novel Highly Efficient/Compact Automotive PCB Winding Inductors Based on the Compensating Air-Gap Fringing Field Concept

The design of power electronic converters is subject to extreme cost pressure, especially in the automotive sector. Consequently, each component needs to be optimized regarding material and manufacturing cost. The latter is especially important for magnetic components, as the expensive wire-wrapping process has a significant impact on the overall production costs. In this article, a new inductor concept is proposed, where the winding is directly integrated into the printed circuit board (PCB), while at the same time the usually large high-frequency conduction losses are mitigated. This is achieved by using the fringing field around a single air gap or several (distributed) air gaps for compensating the adverse magnetic skin and proximity fields within the winding. Consequently, low ac to dc resistance ratios are achieved and the required copper cross-section of the winding can effectively be reduced. Furthermore, a thermal model for the printed circuit board winding is derived, which allows for designing PCB windings close to the thermal limit, and therefore inductors with very high power densities are obtained. Finally, the findings of this article are verified by experimental measurements and a simplified design sequence is described.

Entire Magnetic Integration Method of Multi-Transformers and Resonant Inductors for CLTLC Resonant Converter

An entire magnetic integration methodology of high efficiency printed circuit board (PCB) winding transformer for CLTLC (capacitor-inductor-transformer-inductor-capacitor) resonant converter is presented. All magnetic components in the converter, including two resonant inductors and two transformers, are integrated into an improved EIE (E-type and I-type and E-type) core structure. According to the matrix transformer concept and uneven winding distribution, the novel structure can be obtained by introducing an air gap to the center core leg. Thus, the magnetizing inductance and leakage inductance of the transformer can be controlled easily through adjusting the air gap reluctances. In addition, both the detailed mathematical analysis and the reluctance model of the transformer have been studied. Furthermore, a four-layer printed circuit board winding structure is chosen. The related winding arrangement is also discussed in depth. Finally, a 1 kW prototype with the presented structure is implemented to verify the validity of the theoretical analysis. Experimental results demonstrate that the proposed structure guarantees high efficiency within the entire load range. Peak efficiency of 96.62% can be ensured.

A Review and Comparison of Solid, Multi-Strands and Litz Style PCB Winding

At high frequency, AC resistance of a printed circuit board (PCB) winding becomes important and accounts for a large proportion of planar transformer losses. The winding is then influenced by both skin and proximity phenomenon, which makes the current distribution uneven resulting in an increased resistance. The study of improving AC resistance of a PCB winding has been tackled by many researchers. However, the lack of an overview and comparison among improvements has made it difficult to apply those methods to a specific winding. To overcome the above limitations, this paper investigates the pros and cons of three popular AC resistance optimizing methods: optimizing track width of a solid PCB winding, using multi-strands and using Litz style PCB winding. To verify the theoretical analysis, a total of 12 PCBs are simulated by finite element (FEM) and tested in the laboratory. Five criteria are analyzed, including skin resistance, proximity resistance, AC to DC ratio, total AC resistance and complexity are taken into consideration. The results of this study show that optimizing track width method has a significant improvement on AC resistance while the use of Litz PCB is effective for applications that need stable AC resistance in a wide frequency range. The use of parallel strands winding should be carefully considered as there is not significant benefit in both reducing the AC resistance and AC to DC ratio.

Coupled electromagnetic and thermal analysis of an axial flux permanent magnet synchronous machines with printed circuit board winding

Axial flux permanent magnet synchronous machines (AFPMSMs) with printed circuit board (PCB) windings take on different electromagnetic and thermal performance characteristics when compared to the traditional radial flux permanent magnet synchronous m

Optimizing AC Resistance of Solid PCB Winding

At high frequency, power losses of a winding due to eddy currents becomes significant. Moreover, the skin and proximity AC resistances are influenced by the width of printed circuit board (PCB) conductors and distance between the adjacent tracks which causes many difficulties to design windings with lowest AC resistances. To clarify this phenomenon, this paper focuses on modeling the influence of skin and proximity effects on AC resistance of planar PCB winding, thereby providing guidelines to reduce the winding AC resistance. An approximate electromagnetic calculation method is proposed and it shows that when the winding proximity AC to DC ratio ( F p r o x i m i t y ) is equal to 1 3 the AC on DC ratio caused by skin effect ( F s k i n ) , the winding is optimized and it has lowest AC resistance. 3-D finite element simulations of 3, 7 and 10-Turn windings, which are divided into 3 groups with the same footprint, are presented to investigate the lowest AC resistance when the track width varies from 3 mm to 5 mm and the frequency range is up to 700 kHz. In order to verify the theoretical analysis and simulation results, an experiment with 3 simulated groups, (9 prototypes in total) is built and has a very good fit with simulation results. Experimental results show that at the optimal width, the AC resistance of the windings can be reduced up to 16.5 % in the frequency range from 200 kHz to 700 kHz.

A Linear Position Measurement Scheme for Long-Distance and High-Speed Applications

In the maglev train electric drive system, the linear electric machine is a welcome solution. However, for long railways, the mover position measurement is an issue, especially when the train speed is very high, e.g., 600 km/h. The position measurement method of the mover must be simple and precise at high speeds while maintaining a low cost for industrial applications. The principle of the stator permanent magnet (stator-PM) machine provides evidence that the magnets and windings can be mounted on the mover of the linear resolver, leaving a simple secondary-side structure on the railway. With this idea, this article presents a PM linear resolver that generates orthogonal back-EMFs as the sinusoidal and cosine (SIN/COS) signals. The train position can then be measured by decoding the PM back-EMF. On the other hand, the high-frequency injection is imposed to solve the mover position measurement at zero speed and low speed. This PM linear resolver is prototyped with printed circuit board windings instead of regular coil windings. The dedicated decoding firmware is developed to evaluate the measurement performance up to 60 km/h in the lab setup.

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.

Multiphysics analysis of printed circuit board winding for high‐speed axial flux permanent magnet motor

Gearless and compact motors rotating at speeds above 10,000 rpm are finding many applications nowadays. This study presents the multiphysics modelling and analysis of a multilayer printed circuit board (PCB) stator for high-speed, low-power axial flux permanent magnet motor. The possibility of circulating current in the multilayer PCB is studied. The two major effects of eddy currents at high frequencies: skin effect and proximity effect are investigated for the PCB winding. The losses in the PCB stator are estimated, and thermal analysis is performed to ensure reliable operation of the motor. MagNet 3-D and COMSOL Multiphysics are used, respectively for the finite element analysis and optimisation of the motor; and the simulation results are presented. A prototype of the motor is fabricated and tested to validate the simulation results.