The trend toward high power density, high operating frequency, and low profile in power converters has exposed a number of limitations in the use of conventional wire-wound magnetic component structures. A planar magnetic is a low-profile transformer or inductor utilizing planar windings, instead of the traditional windings made of Cu wires. In this paper, the most important factors for planar transformer (PT) design including winding loss, core loss, leakage inductance, and stray capacitance have individually been investigated. The tradeoffs among these factors have to be analyzed in order to achieve optimal parameters. Combined with an application, four typical winding arrangements have been compared to illustrate their advantages and disadvantages. An improved interleaving structure with optimal behaviors is proposed, which constructs the top layer paralleling with the bottom layer and then in series with the other turns of the primary, so that a lower magnetomotive force ratio m can be obtained, as well as minimized ac resistance, leakage inductance, and even stray capacitance. A 1.2-kW full-bridge dc-dc converter prototype employing the improved PT structure has been constructed, over 96% efficiency is achieved, and a 2.7% improvement, compared with the noninterleaving structure, is obtained.

https://orbit.dtu.dk/files/4566316/Ouyang.pdf

Optimal Design and Tradeoff Analysis of Planar Transformer in High-Power DC–DC Converters

The calculation of a transformer's parasitics, such as its self capacitance, is fundamental for predicting the frequency behavior of the device, reducing this capacitance value and moreover for more advanced aims of capacitance integration and cancellation. This paper presents a comprehensive procedure for calculating all contributions to the self-capacitance of high-voltage transformers and provides a detailed analysis of the problem, based on a physical approach. The advantages of the analytical formulation of the problem rather than a finite element method analysis are discussed. The approach and formulas presented in this paper can also be used for other wound components rather than just step-up transformers. Finally, analytical and experimental results are presented for three different high-voltage transformer architectures.

Self-Capacitance of High-Voltage Transformers

The momentum toward high efficiency, high frequency, and high power density in power supplies limits wide use of conventional wire-wound magnetic components This paper gives an overview of planar magnetic technologies with respect to the development of modern power electronics The major advantages and disadvantages in the use of planar magnetics for high-frequency power converters are covered, and publications on planar magnetics are reviewed A detailed survey of winding conduction loss, leakage inductance, and winding capacitance for planar magnetics is presented so power electronics engineers and researchers can have a clear understanding of the intrinsic properties of planar magnetics

Overview of Planar Magnetic Technology—Fundamental Properties

Parasitic capacitances of conventional transformers can be used as resonant elements in resonant DC-DC converters in order to reduce the overall system size. For predicting the values of the parasitic capacitors without building the transformer different approaches for calculating these capacitances are compared. A systematic summary of the known approaches is given and missing links between the different theories and missing equations are added. Furthermore, a new simple procedure for modelling parasitic capacitances which is based on the known approaches is proposed. The resulting equations are verified by measurements on four different high voltage transformers.

https://www.hpe.ee.ethz.ch/uploads/tx_ethpublications/01518701.pdf

Using transformer parasitics for resonant converters - a review of the calculation of the stray capacitance of transformers

This paper presents a comprehensive physical characterization and modeling of the three-phase common-mode (CM) inductors along with the equivalent circuits that are relevant for their design. Modeling issues that are treated sparsely in previous literature are explained in this paper, and novel insightful aspects are presented. The calculation of the leakage inductance is reviewed, along with the magnetic core saturation issues, and a new expression for the leakage flux path is derived. The influence of the core material characteristics on the performance of the component is discussed, and a new method for the selection of the material for the minimized volume CM inductors is proposed in order to simplify the design procedure. Experimental results which validate the model are presented.

The Three-Phase Common-Mode Inductor: Modeling and Design Issues

This work presents a comprehensive procedure for designing a high output voltage series-parallel resonant DC-DC converter. The system output voltage control is by a combination of duty-cycle and switching frequency variation, where soft-switching is preserved over the entire operating range. The basic principle of operation of the converter is described and an analytical model is established which does provide a basis for the numerical calculation of the stresses on the power components. Furthermore, a control strategy for minimizing the no-load conduction losses is proposed and the transient behavior in case of load steps including output short-circuit is discussed based on digital simulations.

/pdf/design-of-a-5-kw-high-output-voltage-series-parallel-usttbqjic2.pdf

Design of a 5 kW high output voltage series-parallel resonant DC-DC converter

This paper introduces a dimmable electronic ballast for HPS lamps which uses a new strategy to implement the variation of the lamp's power, based on the variation of the switches' duty cycle. The complete operating principle, theoretical analysis and relevant equations are presented in this paper. The experimental results of a 70 W electronic ballast operating at 33 kHz switching frequency are also presented.

F. da Silveira Cavalcante

Papers

Self-Capacitance of High-Voltage Transformers

Design of a 5 kW high output voltage series-parallel resonant DC-DC converter

A new dimmable 70 W electronic ballast for high pressure sodium lamps