Because of the switching action, power electronics converters are potentially large EMI noise sources to nearby equipment. EMI filters are necessary to ensure electromagnetic compatibility. Conventional discrete EMI filters usually consist of a large number of components, with different shapes, sizes and form factors. The manufacturing of these components requires different processing and packaging technologies, of which many include labor-intensive processing steps. In addition, due to the parasitics of discrete components, high-frequency attenuation of the filter is reduced and the effective filter frequency range is limited. As a result, discrete EMI filters are usually bulky, high profile, and have poor high-frequency performance. With an aim to solving these issues, this study explores the integration of EMI filters. The goal is to achieve a smaller size, lower profile, better performance and reduced fabrication time and cost via structural, functional and processing integration.
The key technology for EMI filter integration is planar electromagnetic integration, which has been a topic of research over the last few years. Most of the previous applications of this technology for switch mode power supplies (SMPSs) were focused on the integration of high frequency power passive electromagnetic components, such as HF transformers, resonant/choke inductors and resonant/blocking capacitors. Almost no work has been done on the subject of EMI filter integration. Since the major function of EMI filters is to attenuate, instead of propagate, energy at the switching frequency and its harmonics, the required technology and design objectives are very different from those of other components. High-frequency modeling of the integrated structure becomes more essential since the high-frequency performance becomes the major concern. New technology and a new model need to be developed for EMI filter integration.
To bridge this gap between existing technologies and what is necessary for EMI filter integration, this dissertation addresses technologies and modeling of integrated EMI filters. Suitable integration technologies are developed, which include reducing the equivalent series inductance (ESL) and equivalent parallel capacitance (EPC), and increasing, instead of reducing, the high frequency losses. Using the multi-conductor lossy transmission-line theory, a new frequency domain model of integrated LC structure is developed and verified by experimental results. Through detailed electromagnetic analysis, the equations to calculate the required model parameters are derived. With the developed frequency domain and electromagnetic model, the characteristic of integrated LC modules can be predicted using geometry and material data.
With the knowledge obtained from preliminary experimental study of two integrated EMI filter prototypes, a technology is developed to cancel structural winding capacitance of filter inductors. This can be realized by simply embedding a thin conductive shield layer between the inductor windings. With the…

Integrated EMI Filters for Switch Mode Power Supplies

High-leakage transformers play an important role in power conversion. On-chip, silicon-integrated, and printed-wiring-board-integrated transformers are currently being developed for signal and power applications in high-frequency power supplies. High-power transformers have been developed for the inductive charging of electric-vehicle batteries. These transformers can feature relatively high winding resistances, core loss, and leakage inductances compared with conventional transformers. The conventional open-circuit and short-circuit test calculations have limited use for characterizing these relatively high parasitic transformers. In this paper, the differential (series-opposing) and cumulative (series-aiding) series-coupling tests are developed and applied for the accurate characterization of the transformer resistive and inductive elements. In the series-coupling tests, the various resistive and inductive components simply sum together, making transformer characterization more direct and accurate than attempting to interpret the standard open- and short-circuit (SOS) tests. The SOS tests are extended to provide a more accurate three-measurement approach, and improved correlation is demonstrated between experimental results obtained from the series-coupling tests and the extended open- and short-circuit tests. These results are validated by predictions from finite-element analysis. A sensitivity analysis is carried out to determine the sensitivity of the various test methods to measurement error. The cumulative test is highlighted as being particularly sensitive to measurement error compared with the other test methods.

Comparison of Test Methods for Characterization of High-Leakage Two-Winding Transformers

In the early 1990's, with the boom of the Internet and the advancements in telecommunications, the demand for high-speed communications systems has reached every corner of the world in forms such as, phone exchanges, the internet servers, routers, and all other types of telecommunication systems. These communication systems demand more data computing, storage, and retrieval capabilities at higher speeds, these demands place a great strain on the power system. To lessen this strain, the existing power architecture must be optimized. With the arrival of the age of high speed and power hungry microprocessors, the point of load converter has become a necessity. The power delivery architecture has changed from a centralized distribution box delivering an entire system's power to a distributed architecture, in which a common DC bus voltage is distributed and further converted down at the point of load. Two common distributed bus voltages are 12 V for desktop computers and 48 V for telecommunications server applications. As industry strives to design more functionality into each circuit or motherboard, the area available for the point of load converter is continually decreasing. To meet industries demands of more power in smaller sizes power supply designers must increase the converter's switching frequencies. Unfortunately, as the converter switching frequency increases the efficiency is compromised. In particular, the switching, gate drive and body diode related losses proportionally increase with the switching frequency. This thesis introduces a loss saving self-driven method to drive the secondary side synchronous rectifiers. The loss saving self-driven method introduces two additional transformers that increase the overall footprint of the converter. Also, this thesis proposes a new magnetic integration method to eliminate the need for the two additional iv gate driver magnetic cores by allowing three discrete power signals to pass through one single magnetic structure. The magnetic integration reduces the overall converter footprint. v To my wife Elizabeth Jewel vi (this page intentionally left blank) vii ACKNOWLEDGMENTS With deep appreciation, I would like to thank my advisor, Dr. Fred C. Lee for his guidance, leadership and, and most of all, for inspiring me to be a better engineer. His profound ability to illustrate the logic in research and to drive all of his students to work to their full potential is remarkable. I would also like to thank Dr. Lee for his wonderful attitude and for always having a smile on his face. I am grateful to my committee …

/pdf/compact-isolated-high-frequency-dc-dc-converters-using-self-g0me7bf1hd.pdf

Compact Isolated High Frequency DC/DC Converters Using Self-Driven Synchronous Rectification

This paper describes a new inductive charger circuit for opportunity charging of electric vehicles in the future The coupling transformer utilized features a very large air-gap that is comparable to the cross-sectional dimensions and hasn't been considered in previous studies The study proposes to fully compensate the large leakage inductance of the windings using series capacitors and to control the charging power using an additional DC-DC chopper at the output stage The eddy current losses associated with the leakage flux and voltage stresses in the circuit are shown to be acceptable The working principle of the proposed circuit is experimentally tested

An inductive charger with a large air-gap

The high-frequency transformers used for isolated DC-DC converters tend to have large volume compared with the other components. Therefore, increasing the power density of the transformer is indispensable for increasing the power density of the DC-DC converter. Reducing the dead space of the transformer is one of the effective solutions. It is well-known that the thinly extended core structure reduces the dead space around the transformer formed by the windings protruding to the outside of the core. However, it has not been clarified how much the thinly extended core structure affects the reducing power loss of the transformer. In this paper, the effect of introducing the thinly extended core structure into the transformer is quantified by the optimization of the convertible design parameters of the transformer with systematic round-robin calculation. The result revealed the volume reduction effect by the thinly extended core was greater than the simply dead space reduction effect.

Volume Reduction Effect of Thinly Extended Core Structure for Transformer in Isolated DC-DC Converter

Removing heat from the windings of a high power (>100 kW) transformer is a significant thermal challenge, especially in the case of the ultra-compact electric vehicle inductive charging transformer. In this paper, nine different transformer design techniques are outlined, analyzed and compared for optimization of the primary and secondary winding resistances to minimize copper losses in a high-power, high-frequency transformer. For the inductive charging transformer example illustrated, these techniques reduce the total winding losses by as much as 5 to 1 and the AC winding losses by 14 to 1. The techniques used are a mixture of well-known approaches, such as winding interleaving, and other lesser-known approaches, such as flux shaping. The winding losses are calculated using a two-dimensional finite element analysis (FEA) program, and using one-dimensional equations for comparative purposes. These techniques result in a high-power transformer with a power density greater than 1300 W/in/sup 3/.

Optimizing AC and DC winding losses in ultra-compact, high-frequency, high-power transformers

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Optimizing AC and DC winding losses in ultra-compact, high-frequency, high-power transformers