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Modeling power electronic converters becomes even more important in systems such as microgrids. These models are very useful for dynamic interaction among converters and stability analysis. This paper proposes a black-box approach to obtain an equivalent switching model of open and closed loop converters. The information needed to apply this method is a general knowledge about the converter topology. Then, the parameters are identified by employing a combination of the particle swarm optimization and the genetic algorithm. The proposed approach is validated by means of detailed simulations and experimentally using a buck and a boost converter. The advantage of the approach is that, with just minimum information regarding converter topology, it is possible to obtain a very accurate switching model which inherently accounts for the nonlinearities caused by the switching nature of the converters, which is key for nonlinear stability analysis.

BackgroundThe clinical outcome of the most common therapeutic options of rheumatoid arthritis (RA) patients, such as conventional disease-modifying antirheumatic drugs (DMARDs) and TNF inhibitors (TNFi) is still unpredictable, since a high percentage of patients do not response to the therapy. Innovative analyses combining high-throughput technologies and thorough clinical assessments are needed to gain insight about the management of this prevalent autoimmune disorder.ObjectivesTo evaluate the systemic inflammatory proteome of RA patients, to identify useful biomarkers associated with distinctive clinical outcomes.MethodsSerum samples from 140 subjects, including 40 healthy donors (HC) and 100 RA patients with high activity disease (mean DAS28=4.7), were profiled with the innovative proteomic methodology “proximity extension assay” (Olink) which analyses one panel of 92 pro-inflammatory proteins. Samples from RA active patients included 40 from newly-diagnosed RA patients before taking conventional DMARDs and 60 from biologics-naïve patients (mean disease duration=10 years) before receiving TNFi drugs. Clinical outcomes were evaluated following EULAR criteria after 6 months of treatment and patients were classified as responders or non-responders to the different therapeutic interventions. Unsupervised hierarchical clustering methodologies were applied to identify subgroup pf patients based on the proteomic profiles. Gene ontology enrichment were used to interrogate the biological meaning of the distinctive molecular signatures identified.ResultsThe inflammatory proteome analysis identified 33 proteins differentially expressed and upregulated in RA patients compared with HC including several chemokines (CCL-11, -19, -20, -23, -28; CXCL-10, -11, -9; MCP-1, -3), interleukins (IL-6, -8, -18, -10, -17c), and other relevant proinflammatory mediators (VEGFA, CD40, MMP-1, CSF-1, OPG, FGF23) among others (FDRThe unsupervised clustering analysis using the proteomic profile of RA patients before TNFi identified two subgroups of patients. Cluster 1 (C1) was characterised by patients with higher levels of several pro-inflammatory mediators compared with Cluster 2 (C2), where a signature of 16 chemokines was significantly enriched (CCL-3, -4, -10, -11, -20, -23; CX3CL1; CXCL-1, -10, -11, -5, -6, -9; MCP-1, -3, -4). Clinically, 25% of the non-responders’ patients was included in C2, while 75% was located in C1, suggesting that a prominent circulating chemotaxis profile prior therapy is associated with a poor clinical outcome. These data were similarly observed in patients before receiving DMARDs, where a signature of upregulated chemokines and pro-inflammatory mediators characterised a cluster with a high % of non-responder patients.ConclusionA pro-inflammatory signature, where chemokines are predominantly up-regulated in the serum of RA patients before therapy, is associated with a poor clinical outcome. This newly identified signature, which deserves a more in-depth analysis, might be clinically useful guiding precision medicine and novel therapeutic approaches.AcknowledgementsSupported by ISCIII (PI21/005991 y RICOR-RD21/0002/0033) co-financed by FEDER, Fundacion Andaluza de Reumatología (FAR) and Consejería de Conocimiento, Investigación y Universidad de la Junta de Andalucía (P20_01367).Disclosure of InterestsNone declared.

Maritime applications have found in the integration of the electric power system a way to further improve efficiency and reduce the weight of new electric ships. This movement has led scientists to integrate smart management systems to optimize the overall behavior of the grid. In this context, power electronics play a key role in linking the different elements of the power architecture. Moreover, the transition toward a dc distribution, which has already been established in other applications, is being regarded as a promising alternative to ease the integration of renewable sources, batteries, and the ever increasing number of dc loads. In this paper, blackbox models are proposed as a tool to foresee the effect of these complex interactions, overcoming the lack of detailed information about the power converters. Large-signal strategies are proposed in order to consider nonlinearities in the static and dynamic behavior of the converters. An accurate model of the physical layer is essential to allow intelligent systems to take the most out of the system performance. This approach offers the opportunity to study the dynamic response of complex interconnected systems, tune the system-level controllers, design protections, or assess the compliance of the system dynamics with the standards. Experimental results are included in order to validate the proposed method.

EPCs (Electronic Power Converters) are the key elements of the smart dc microgrid architectures. In order to enhance the controllability of the system, most of the elements are envisioned to be connected to the different buses through EPCs. Therefore, power flow, stability, and dynamic response in the microgrid are function of the behavior of the EPCs and their control loops. Besides, dc microgrids constitute a new paradigm in power distribution systems due to the high variability of their operating conditions, owing to the intermittent behavior of the renewable sources and customer energy consumption. Furthermore, in order to deal with this variability, the power converters can modify their operation mode, adding complexity to the dynamic and stability analysis of the system. This paper gives an overview of the various analytical and blackbox modeling strategies applied to smart dc micro/nanogrids. Different linear and nonlinear modeling techniques are reviewed describing their capabilities, but also their limitations. Finally, differences among blackbox models will be highlighted by means of illustrative examples.

DC electric power distribution is becoming popular due to the proliferation of renewable sources and storage elements in applications such as electric vehicles, ships, aircrafts, microgrids, etc. These systems are characterized by a high integration of power electronic converters. From a system-level perspective, it would be desirable to design this kind of systems using commercial-off-the shelf converters. However, in general, the manufacturers do not provide a behavioral model of the devices in order to analyze the dynamic behavior of the interconnected system before the actual implementation. In the literature, several blackbox modeling techniques have been proposed to overcome this lack of information. This paper proposes the integration of dynamic weighting functions to the polytopic model in order to improve the accuracy of the behavioral models when the input variables change sharply. A boost converter is used as case study and the performance of the proposed model is compared with the most relevant techniques that can be found in the literature.

The power electronic based dc distribution systems are becoming an interesting solution in many applications as electric vehicles (automobiles, planes, ships, etc.), data centers, and microgrids. On the one hand, due to the complexity and the amount of these installations, the use of sophisticated commercial-off-the-shelf converters is very convenient. On the other hand, the use of commercial converters complicates the system-level analysis of these systems, due to the lack of detailed information about the dynamic response of these devices. A solution to this issue is the blackbox modeling approach, which is able to identify behavioral models of the converters from their response to specific tests. However, the approaches available in the literature are not able to account for strong nonlinear dynamic behaviors, such as the ones shown by converters with discontinuous and continuous conductions modes or the ones that integrate different control modes. In this paper, a blackbox Parameter Varying Transfer Functions (PVTF) model is proposed in order to obtain very accurate models of commercial converters in dc microgrid applications.

Career situation of first and presenting author Young investigator. Introduction Currently there is very little information on optimal levels of golimumab in patients with polyarthritis. Objectives The main objective was to analyze the minimal serum concentration of golimumab (GOL), anti-golimumab antibodies (AcGOL) and its relation to the activity of the disease measured by DAS 28 index, in rheumatoid arthritis (RA) and psoriatic arthritis (PA). Methods We conducted a retrospective observational study with RA or PA patients on golimumab treatment between 2011 and 2016. We analized the age, sex, diagnosis, dose, dose interval, duration of treatment, concomitant disease modifying drugs (DMARs), minimum concentration of GOL (GOL Cmin), AcGOL and DAS28 levels. Sampling was performed on the day corresponding to the dose of golimumab, prior to administration, in order to obtain the minimum levels of the drug. The analytical technique used for the determination was the Promonitor® sandwich ELISA. Results 10 RA, 5 AP patients were selected. Median age 53 years. 67% women. All with golimumab 50 mg with an administration interval of 28 to 41 days. Duration of treatment 16.73 months (median). 80% underwent combination therapy with DMARDs. Only one patient (RA) presented levels of AcGOL, with undetectable Cmin, DAS28 of 4.05. Golimumab levels in patients without AcGOL and DAS28 3.2 were: 2 Cmin Conclusions Very variable GOL Cmin values ( Disclosure of Interest None declared.

This paper introduces a new approach of black-box modelling of bidirectional battery chargers for Electric Vehicles (EV). Due to the increasing penetration of EV, the number of battery chargers connected to the grid is also increasing, being a challenge to assess the impact of such growing number of battery chargers into the grid performance. The black-box model is able to represent the behavior of the battery charger using the information generated from a number of tests applied to the equipment to be modeled. Due to the variability of the operating conditions a large-signal modelling strategy based on the polytopic structure is proposed. This modelling strategy will be tested with an actual commercial bidirectional battery charger. The experimental tests of the paper illustrate the Grid to Vehicle (G2V) and Vehicle to Grid (V2G) operations.

This paper proposes a black box modelling strategy for a bidirectional battery charger (BBC) for Electric Vehicles (EV) 1 , either the BBC is operating in the vehicle to grid (V2G) mode or not. Due to the increasing penetration of EV, the number of battery chargers connected to the grid is also increasing, being a challenge to assess the impact of such growing number of battery chargers into the grid performance. At the same time, there is no detailed information (static and dynamic) of the commercial chargers used in EV and connected to the grid. In this approach, a behavioural black box model is proposed. The generation of the model requests for performing a number of simple tests to the BBC in order to identify the model parameters. In the paper, a detailed switching model in PSIM is used as the actual BBC. The model thoroughly tested by simulation, and compared with the results of the generated black box model and the detailed switching model used as a reference.

The cascade connection of converters can have destabilizing effects on the response of the system due to the behavior of controlled converters as constant power load (CPL). It is prevailing to simplify the point-of-load (POL) converters as CPLs. The CPL simplification is a low-frequency approximation that assumes that there are no dynamic interactions between interconnected converters. However, the dynamic interaction between converters is another source of instability that must be taken into account. Furthermore, the dynamic interaction between converters can be very sensitive to parasitic elements within the converters; hence the results in real applications can differ substantially from analytical estimations. As a result, studying of detailed models can bring about a better understanding of stability analysis. In order to cope with these phenomena, the most accurate result comes from black-box models of the converters around different operating points obtained by the injection of perturbations to the actual converters and the application of identification tools. This black-box model result is equivalent to the averaged analytical model but it is able to account for the actual values of the parasitic elements. This paper compares the performance of the stability analysis with a CPL approximation with a detailed model of the POL converter. Moreover, the sensitivity of parasitic elements of the POL converter will be exposed.

DC microgrids are envisioned to be EPDS (Electronic Power Distribution Systems) composed of COTS (Commercial-Off-The-Shelf) converters. Naturally, these converters will determine the dynamic behavior of the system. Besides, unlike classic EPDS, microgrids are highly variable due to the intermittent behavior of the renewable sources and customer consumption. In this context, there is not an accepted solution when it comes to create a model able to account for the large-signal dynamic behavior of the converters, their different operation modes or the interaction among them, which could lead to dynamic degradation or even instability. This work proposes the blackbox polytopic model as a tool able to accomplish these objectives. In particular, it is proposed a methodology to derive dynamic weighting functions using the characteristic polynomial of the transfer functions identified. Using this method, strong nonlinearities as transitions between operation modes can be represented more accurately and with a deterministic approach. This is a step forward towards the complex task of defining an automated tool able to model the particular phenomena that arise in dc microgrids.

Modern electric power distribution systems are progressively integrating electronic power converters. However, the design of electronic-power-converter-based systems is not a straightforward task, as the interactions among the different converters can lead to dynamic degradation or instabilities. In addition, electric power distribution systems are expected to consist of commercial-off-the-shelf converters, which implies limited information about the dynamic behavior of the devices. Large-signal blackbox modeling approaches have been proposed in order to obtain accurate dynamic models of commercial converters that can be used for system-level analyses. However, most of the works are focused on DC-DC converters. In this work, a large-signal blackbox model is proposed to model grid-connected three-phase DC-AC converters. An experimental setup has been used to demonstrate the limitations of small-signal models and the capability of the proposed modeling approach to capture the dynamic behavior of the converter when large perturbations are applied. Finally, the automation of the model identification process is discussed.

Microgrids are a growing trend toward a new power distribution system that allows for a high penetration of renewable distributed generation, electrical energy storage systems and controllable loads. This modern concept exploits the advances in electronic technology to improve efficiency, reliability, and flexibility, while reducing cost and size. Furthermore, microgrids can operate in a grid-connected mode or in an islanded operation mode. Electronic power converters are essential in this kind of architecture in order to interface every element to the system. They introduce controllability into the system and dynamic decoupling. However, the control of these elements from a system-level perspective remains a challenge. The dynamic interaction among the power converters, their variable operation modes, and the lack of information about commercial converters, are some of the factors that complicate an integrated analysis. This work proposes a large-signal black-box modeling approach able to characterize the nonlinear behavior dc/ac converters. The study is particularized to a converter interfacing a renewable source with the grid. Nevertheless, this methodology can be extended to different operating modes. The performance of the model is compared with the detailed switching model of the converter.

The huge progress of power electronics technology along last decades opens extraordinary new possibilities for the electric grid. Some examples of what can be achieved with the incorporation of electronic power converters in the system are the penetration of RS (renewable sources) and storage, boosting reliability and power quality, and integrating consumers as part of the system. However, there are still some challenges ahead before the massive deployment of Smart Grids. Lately, a lot of research has been carried out on converters topologies and control strategies in order to get the most out of the microgrids. Therefore, there is a need for methodologies that allow designers to foresee the behavior of these systems comprised of several different power converters governed by the proposed control strategies. In this context, this paper studies the performance of the polytopic models for the analysis of commercial power converters working in dc microgrids. This is a nonlinear modeling technique which integrates small-signal models obtained in different operation points by means of suitable weighting functions. Furthermore, the linear local models can be obtained in a blackbox fashion using suitable two-port models as can be the G-parameters models. This work particularly focuses on the analysis of different power converters using the well-known dc bus signaling control strategy. Thus the modeling of the diverse possible states in which this control technique can operate, and more important the transitions among them, are investigated. In addition, the feasibility of applying system level control techniques to the polytopic models of the converters, such as current sharing or voltage restoration, is considered.

During the last few decades power converter-based systems have become a very interesting solution for electric power distribution in many applications. They have been successfully implemented in ships and “more electric aircrafts”, replacing some of the mechanical and hydraulic systems for power converters in order to optimize the efficiency and reliability of the vehicles. They have been also applied to UPS (Uninterruptible Power Systems) for applications where the efficiency or the security of supply is mandatory as in hospitals and data centers. More recently, these architectures have been proposed for Smart Grids. An important advantage of using power converters is the possibility of dynamical independence between different parts of the system. Therefore these different parts can be studied individually, drastically simplifying the analysis of large systems. However, the analysis of these parts is not straightforward, since the interconnection of power converters produces interaction between them, which can lead to dynamical degradation or even instability. This analysis is often performed by system designers, who usually do not have information about the internal architecture of the converters. Besides, the power converters behavior is operating point dependent, so in many cases small-signal techniques are not enough for these applications. Therefore, in order to cope with these issues, this paper proposes a blackbox large signal stability analysis based on the Lyapunov method.

In the last years, the use of distributed uninterruptible power supply (UPS) systems has been growing into the market, becoming an alternative to large conventional UPS systems. In addition, with the increasing interest in renewable energy integration and distributed generation, distributed UPS systems can be a suitable solution for storage energy in micro grids. This paper depicts the most important control schemes for the parallel operation of UPS systems. Active load-sharing techniques and droop control approaches are described. The recent improvements and variants of these control techniques are presented.

The smart grid concept is increasingly becoming popular within the academia and industry. The integration of electronic power converters as an enabler for the massive deployment of distributed renewable energy sources, along with the inclusion of control, monitoring and automation systems in the grid, has drawn the attention of many researchers. Furthermore, a transition towards dc distribution is currently under investigation due to its more suitable interface with most of the modern loads and sources, which offers benefits in terms of size, cost and reliability of the whole system. This paper proposes a black-box polytopic modeling approach as a tool for the system-level design of dc based nanogrids. This strategy allows both small and large-signal analysis of power distribution systems even when commercial off-the-shelf converters have to be integrated. In addition, the main characteristics of the dc bus signaling control, i.e. droop control, changes in power converter control mode and disconnection of loads, have been incorporated in the modeling structure.

The energy consumption in mobile systems has become a big challenge that limits high performance and autonomy in mobile systems. The dynamic voltage scaling (DVS) is a recent technique that reduces energy consumption varying dynamically the supply voltage of the system accordingly to the clock frequency. The buck topology is a good candidate to supply step variations of the output voltage meeting the DVS requirements. In this paper, it is analyzed which is the fastest output voltage evolution that can provide the Buck topology. The minimum time state transition in the buck converter and its corresponding control law are obtained applying the maximum principle or Pontryagin's principle. Design criteria for the buck topology are derived from this result. The analysis is extended to a multiphase buck converter. The minimum time control law is validated in a prototype. The measurements are in good agreement with the theoretical results.

Nowadays, uninterruptible power supply (UPS) systems are in use throughout the world, helping to supply a wide variety of critical loads, in situations of power outage or anomalies of the mains. This article describes the most common line problems and the relationship between these and the different existing kinds of UPS, showing their operation modes as well as the existent energy storage systems. It also addresses an overview of the control schemes applied to different distributed UPS configurations. Finally, it points out the applicability of such systems in distributed generation, microgrids, and renewable energy systems.

Objetivo Hay pocos estudios sobre las manifestaciones osteomusculares tras un trasplante alogenico de progenitores hematopoyeticos (TPH-ALO). El objetivo del presente estudio es investigar los sintomas osteomusculares observados tras la realizacion de un TPH-ALO como tratamiento de distintas enfermedades hematologicas y no hematologicas. Material y metodos Estudio observacional retrospectivo, realizado mediante la revision de historias clinicas. Resultados Desde el ano 1996 hasta el 2000 se identifico a 123 pacientes sometidos a un TPH-ALO, 34 ninos (5 meses-14 anos) y 81 adultos (15-55 anos). La distribucion por sexos fue la siguiente: 48 mujeres (39%) y 75 varones (61%). De estos pacientes, 43 (34,90%) presentaron enfermedad del injerto contra el huesped (EICH) aguda, 33 de 106 (31,1%) presentaron EICH cronica y 50 de los pacientes (40,65%) murieron durante el seguimiento. Catorce (13,2%) presentaron manifestaciones osteomusculares: 6 (5,6%) necrosis aseptica, 5 (4,7%) esclerodermia, uno artralgias y bronquiolitis obliterante, uno poliartralgias y otro monoartritis de rodilla. Conclusiones Es dificil atribuir los sintomas osteomusculares tras un TPH-ALO a una sola causa. Las manifestaciones inflamatorias y fibrosantes pueden ocurrir debido al proceso inflamatorio de la EICH cronica o por los tratamientos administrados durante el procedimiento.

New recommendations and future standards have increased the interest in power factor correction circuits. There are multiple solutions in which line current is sinusoidal. In addition, a great number of circuits have been proposed with nonsinusoidal line current. In this paper, a review of the most interesting solutions for single phase and low power applications is carried out. They are classified attending to the line current waveform, energy processing, number of switches, control loops, etc. The major advantages and disadvantages are highlighted and the field of application is found.

The magnetic field in many magnetic components, namely toroids and EE cores, has a three-dimensional (3-D) distribution. Energy and losses calculation in these particular structures makes necessary the use of 3-D techniques that accounts for all 3-D effects. The calculation of the energy and losses is needed in order to obtain any transformer model. This paper presents a procedure that allows the calculation of energy and losses in 3-D structures using two-dimensional (2-D) approaches. This procedure accounts for 3-D effects, solving each magnetic component by means of two different analyses but using 2-D finite-element analysis (FEA) solvers instead of 3-D. The main advantages of this procedure are that all geometrical and frequency effects are taken into account using 2-D FEA solvers. 3-D FEA solvers are not applicable to analyze most practical cases because of the complexity in the geometry. Therefore, the use of this method is not only advantageous from the point of view of time reduction, but also it is a solution for many cases where 3-D solvers are not a feasible solution. Some experimental results illustrate the application of the methodology, which is especially useful to study the influence of the winding strategy in toroidal structures and to design integrated magnetics in order to adjust the coupling coefficient between each pair of windings before the component construction.

Nowadays, most digital controls for power converters are based on DSPs. This paper presents a field programmable gate array (FPGA) based digital control for a power factor correction (PFC) flyback AC/DC converter. The main difference from DSP-based solutions is that FPGAs allow concurrent operation (simultaneous execution of all control procedures), enabling high performance and novel control methods. The control algorithm has been developed using a hardware description language (VHDL), which provides great flexibility and technology independence. The controller has been designed as simple as possible while maintaining good accuracy and dynamic response. Simulations and experimental results show the feasibility of the method, opening interesting possibilities in power converters control.

A power electronics circuit allows the generation of high-frequency magnetic field that can be used to increase the temperature of cancer cells previously invaded with the magnetic nanoparticles. The circuit designed for this purpose is a high-frequency phase-shift inverter implemented with SiC devices and natural zero voltage switching. The inductive load has been optimized to increase as much as possible the magnetic field at the center of it considering the physical restrictions. Into this inductor, an adiabatic probe filled with nanoparticles is placed being the main objective to increase its temperature. The control of the inverter has been designed in such a way that it is easy to try waveforms different from the classical sine waves to see its effect on the temperature of the sample. Although the research is in one of the early stages, the first conclusions about the optimal frequency and field have been obtained showing that this technique could be a real option in the future.

In this paper, a simple single-stage AC/DC converter based on the flyback topology is presented. With a single switch, a fast-regulated output voltage is achieved and, although the line current is not sinusoidal, the converter complies with the Standard IEC 1000-3-2 about low frequency harmonies for a medium power range (50-500 W). The major advantages of this converter are the size and the efficiency. Design guidelines, analysis of the line current, and extensions to other topologies are analyzed. Experimental results are included in the paper.

Single winding self-driven synchronous rectification (SWSDSR) approach is a new driving circuit that overcomes the limitations of the traditional driving schemes, becoming an interesting alternative to supply new electronic loads such as microprocessors. Traditional self-driven synchronous rectification (SDSR) technique has shown very good performance to improve efficiency and thermal management in low-voltage low-power DC/DC converters, however it can not be extended to the new fast dynamic, very low voltage applications. SWSDSR scheme is based on an additional winding in the power transformer (auxiliary winding). It allows for maintaining the synchronous rectifiers (SRs,) on even when the voltage in the transformer is zero, which is impossible to do in traditional self-driven approaches. It also makes it possible to drive properly the SRs even in very low voltage applications, 1.5 V or less. Coupling of the windings strongly affects the performance of the SWSDSR technique. The influence of the coupling between the different windings is analyzed through simulations of different transformers designed for the same application. Models of transformers are generated with a finite element analysis (FEA) tool. Goodness of the SWSDSR scheme is validated through experimental results.

AC/DC is one of the most common power conversions in power electronics, DC loads should be fed with a stable and a tight regulated voltage. At the same time, the AC/DC converter should comply with low-frequency harmonic regulation. The classical two-stage AC/DC converters achieve these two objectives, although the overall efficiency is low because the power is processed twice. An alternative solution is presented in this paper. It is based on the division of the input power in two parts, one of them processed only once and keeping a unity power factor. This strategy improves the efficiency and reduces the size of the converter without any complex control scheme. This proposal can be implemented with a great variety of well-known topologies. The experimental results show that this solution is a good tradeoff between efficiency and size.

Sepic and Cuk power converters working as power factor preregulators (PFP) in the discontinuous conduction mode (DCM) present the following desirable characteristics for a PFP: (1) the power converter works as a voltage follower (no current loop is needed); (2) the theoretical power factor is unity; and (3) the input current ripple is defined at the design stage. Besides, input-output galvanic isolation is easily obtained. This paper analyzes the operation of both power converters as DCM-PFP. Design equations are derived, as well as a small-signal model to aid the control loop design. Both simulation and experimental results are presented that are in agreement with the theoretical analysis and complement the work.

Distributed power supply systems are an attractive solution to meeting the requirements (redundancy, modularity, battery backup, etc.) for the next generation of power supply systems. In addition, the normalization regarding power factor and total harmonic distortion (THD) makes it necessary to include power factor correction in the input stage in such architectures. This paper presents a novel approach of an integrated battery charger/discharger which offers power factor correction and battery galvanic isolation in a simple structure. Placing the battery in the primary side overcomes the need of galvanic isolation integration in each of the DC/DC on-board power converters when this topology is used as part of a distributed power supply system.

This paper summarizes some of the current solutions to fulfil the requirements of the new low voltage power systems. On one hand, microelectronics evolution demands lower supply voltage. On the other hand, the portability of the new communication systems demands lighter and smaller power electronics. The improvement of the performance of low power and low output voltage converters is carried out in this paper. Topics like power density, efficiency, thermal management, battery life, hard and soft switching, magnetics integration, synchronous rectification and power factor correction affect each other in these kinds of converters. Although all the relations among the previous terms are difficult to assess, this paper reviews some aspects of the current situation.

An alternative to the use of a conventional magnetic amplifier in the control of a second output in buck derived DC-to-DC converters is presented. Power semiconductors in the active region are avoided and the second output does not present additional phase shift due to the rest of the core system. These two advantages increase converter efficiency and transient response. The method is based on a double modulation of the switching frequency and duty cycle in the power switch. The switching frequency modulation is, however, relatively small. Keeping the switching frequency almost constant versus input voltage variations and changing slightly versus load variations. >

The Single Ended Primary Inductance Converter (SEPIC) presents several advantages over boost and flyback topologies which make this converter very convenient to be used as Power Factor Preregulator...

Engineering is changing as a consequence of scientific and technological evolution and society needs and demands. Engineers need to understand the structure and behaviour of matter from nanoscale to extremely complex systems. Convergence of scientific and technological disciplines requires also an interdisciplinary approach in education. In this presentation some of the challenges and possible orientations in Engineering Education will be discussed.

Background The frequency of stroke in SLE patients between 18–44 years is 2 times the frequency in general population of the same age and sex. Clinical atherosclerosis is detected in 6%–12% of patients with SLE. Some researchers have suggested that the development of atherosclerosis may be related to the systemic inflammation. The objetive of our study is to assess cardiovascular risk in patients with SLE by measuring carotid intima-media thickness and identifying the presence of plaques. Material and methods Cross-sectional study on a series of 10 SLE patients without dyslipidemia. The presence of plaques and/or an intima-media thickness higher than 0.9 mm, evaluated with a high-resolution B mode ultrasound, reflect high cardiovascular risk. Results Of the 10 patients, 8 were women. The mean age was 36 ± 1.2 years and the mean age at diagnosis of the disease 23.2 ± 7.37 years. The patient’s characteristics and analytical data are shown in table 1. Mean intima-media thickness in the right carotid was 580.72 ± 103.83 mm and in the left 544.76 ± 202.17 mm. Of the 10 patients, 3 had plaques, 2 of them were smokers and had been treated with Rituximab after unsuccessfully treatment with several immunosuppressants. Conclusions The 30% of our patients had plaques, even without having classical cardiovascular risk factors. The use of carotid ultrasound may predict cardiovascular events. Carotid study may be considered for assessing the existence of subclinical aterosclerosis in SLE patients and treating with statins when necessary.

Magnetic integration and magnetic coupling are very promising concepts to be applied in multiphase converters. Tight magnetic coupling allows energy transfer among phases. Ideally the magnetic component can act as a voltage source, with very low output impedance and with a perfect sharing of output current ripple. The main advantages provided by magnetic coupling are size and losses reduction and dynamic improvement. In this paper two winding transformer arrangements to be used in multiphase converters are presented, and validated with a new integrated transformer.

Digital controllers are becoming an important alternative to the traditional analog solutions employed for controlling switching power converters. Among digital controllers, microprocessor-based implementations (such as DSPs) are the most usual ones. However, custom hardware implementations (FPGAs and ASICs) are obtaining special attention for their advantages in some applications, derived from their concurrency and high processing speed. These solutions are still less usual because of two main drawbacks: lack of knowledge by the designers and no methodology to follow. This work focuses on the second point, proposing a methodology to design custom hardware controllers for switching power converters.

Since the temperature rise is one of the key parameters in the design of magnetic components, thermal models are commonly applied in order to calculate the temperature value. Finite element analysis (FEA) tools are typically used to visualize thermal distributions but not for obtaining a model from the field calculation. This work presents a new thermal model based on the use of a thermal network whose parameters are obtained from 2D/3D FEA analyses. The model is suitable for any geometry and any thermal distribution. Comparisons of the proposed model with measurements and FEA simulations are also presented.

Piezoelectric transformer (PT) design requires finite element analysis (FEA) tools, because its performance depends strongly on its shape (2D/3D effect). The main drawback of these tools is that they do not provide the electrical model needed to design the power converter. Nevertheless, the existing electrical models only take into account the main direction of vibration (1D). In this paper, a procedure to improve 1D model parameters by taking into account FEA tool information is proposed.

Piezoelectric transformers (PTs) provide several advantages compared to magnetic components that are higher power density, lower radiated noise and higher voltage isolation capability. PT must be properly designed to benefit the power converter with the advantages aforementioned. In this paper, a step by step procedure to determine the electrode area, the type of material, the number and thickness of the layers and the electrode distribution considering power topology restrictions is presented.

This paper shows the goodness of the multiphase half bridge topology (two phases) for high input voltage (48 V), low output voltage (2 V) and high efficiency applications. The power stage is designed with a high current speed capability (20 A//spl mu/s) to reduce the size and cost of the output capacitors. The strong influence of the dynamics specs on the design of the power stage is analyzed in detail. Average current mode control is applied to assure current sharing between both phases and feed-forward of the load current (Richard Redl et al. 1986) is used to maximize the dynamic response of the average current mode control. Performance of this control method are explored and compared with other techniques.

Analytical magnetic models are used when the winding strategy and the geometry of the magnetic component produces an 1D magnetic field distribution. Additionally, analytical thermal models can be used when thermal distribution, the geometries of the windings and the core produce an 1D heat flux distribution. This work shows how both thermal and magnetic analytical models can be coupled to obtain an accurate global model that allows magnetic designer the optimization of the magnetic component for a specific application based not only in magnetic information like maximum flux density, magnetic losses, etc, but also in thermal concepts like maximum temperature rise, heat flux, etc. The proposed approach is validated using finite element analysis and measurements.

Next future vehicles will change battery voltage front 14 to 42 V. As a consequence, new converters are being developed to cover the needs of the electrical circuits. In the meantime, vehicles will have dual battery system (14 and 42 V). A 1 kW bidirectional 14-42V DC-DC converter has been built and tested for these vehicles. The goodness of the digital control allows the use of a high number of interleaved converters, yielding to a low profile (10 mm height) circuit without current sensing.

This paper presents a very simple step-down DC/DC low power converter based on piezoelectric transformers (PTs) without any magnetic component. PTs become very interesting in this kind of applications comparing with magnetic transformers due to the higher power density. It is important to highlight that the PT has been specifically designed to avoid the use of magnetic components. Dynamic response of the power stage with the PT is analyzed, achieving a 2.5 kHz bandwidth. The use of a PT allows a wide input voltage range (20 V-75 V), 3 V, 1 W DC/DC converter.

In this paper several techniques for integration of magnetic components in interleaved converters are analyzed. Magnetic components define the way the energy is transformed. Several opposite approaches can be considered: from decoupled integrated inductors to tightly coupled inductors. The integration of inductors in the same core for multiphase converters is especially analyzed from the point of view of size, losses and coupling.