Miguel J. Prieto

Design and analysis of thick-film integrated inductors for power converters

This paper describes the design procedures followed to obtain a thick-film inductor for its application in DC/DC power microconverters. The main characteristics of the new technology used are commented upon and design equations are given. Results are compared to those obtained by means of finite-element analysis tools. Details of some thick-film inductors developed with this technique (within the framework of the IMPASS Esprit Project (number 23910), financed by the European Community) are also given. The inclusion of one of these inductors in a 5-to-3.3-V DC/DC converter contributes to obtaining a very high power density: 6.25 W/cm/sup 3/.

A very simple DC/DC converter using piezoelectric transformer

Piezoelectric transformers (PTs) have lately been looked upon as an attractive solution to reduce size and weight in AC/DC converters. This paper presents a topology that includes such a device while minimizing the number of additional components required for an adequate performance. An 8-watt AC/DC adapter (110 V/sub AC/, 12 V/sub DC/) operating at frequencies around 500 kHz is obtained using this topology.

A multiwinding modeling method for high frequency transformers and inductors

This paper presents a method to obtain an electric model for transformers and inductors, including both frequency and geometry effects in the windings, which can be linked with existing core models. One-dimensional distributions for magnetic and electric fields are assumed, and from Maxwells equations an equivalent electric circuit is easily obtained. This equivalent circuit has been included in analog simulators (Spice, AnalogWorkBench, Saber ...), and comparisons between measured and simulated results are shown, both in time domain and in AC sweep, which verify the model accuracy. The model described in this paper allows designers to deal with key issues in the design of high-frequency magnetic components (copper losses, leakage inductance, skin and proximity effects) by using analog simulators, which are usually more familiar to them than finite-element analysis tools.

New active input current shapers to allow AC-to-DC converters with asymmetrically driven transformers to comply with the IEC-1000-3-2

Four new topologies of active input current shapers (AICSs) for converters with symmetrically driven transformers (such as half-bridge, full-bridge and push-pull) have been proposed. This paper analyzes the extension of the use of these new AICSs topologies to converters with asymmetrically driven transformers. Using some of these topologies, the size of AICS inductors can be reduced and even integrated in a single magnetic core. As in the case of other converters with AICS circuit, the new topologies allow line current harmonics to be reduced and thereby to comply with the IEC 1000-3-2 specifications, whilst maintaining all the features of standard DC-to-DC converters (e.g., fast transient response). Finally, the proposed topologies have been experimentally tested.

New topologies of active input current shapers to allow AC-to-DC converters to comply with the IEC-1000-3-2

This paper deals with the analysis of four new implementations of the recently proposed active input current shaper (AICS). These new implementations of AICS can be used with DC-to-DC topologies in which the voltage across the transformer is either a symmetrical waveform (e.g. half-bridge, push-pull or full-bridge) or an asymmetrical waveform (e.g. forward, flyback, SEPIC, Cuk or Zeta). Using some of these implementations, the size of the AICS inductors can be reduced and even integrated in only one magnetic core. As in the case of other converters with AICS, the new implementations allow us to reduce the line current harmonics in order to comply with the IEC 1000-3-2 specifications, maintaining all the features of standard DC-to-DC converters (e.g. fast transient response). Finally, the proposed topologies have been experimentally tested.

Influence of transformer parasitics in low-power applications

High-frequency operation of power converters has made it clear that the parasitic components associated with power transformers have an important influence on the behavior of the converter. Leakage inductance is often considered to be the most important parameter to take into account when designing a transformer. However, when dealing with low-power applications, self-capacitance and mutual capacitance values may play a much more important role. A proper understanding of the influence of these parasitic components and a method that allows determination of their values will help designers optimize their power converters.

Development of a wireless sensor network for individual monitoring of panels in a photovoltaic plant.

With photovoltaic (PV) systems proliferating in the last few years due to the high prices of fossil fuels and pollution issues, among others, it is extremely important to monitor the efficiency of these plants and optimize the energy production process. This will also result in improvements related to the maintenance and security of the installation. In order to do so, the main parameters in the plant must be continuously monitored so that the appropriate actions can be carried out. This monitoring should not only be carried out at a global level, but also at panel-level, so that a better understanding of what is actually happening in the PV plant can be obtained. This paper presents a system based on a wireless sensor network (WSN) that includes all the components required for such monitoring as well as a power supply obtaining the energy required by the sensors from the photovoltaic panels. The system proposed succeeds in identifying all the nodes in the network and provides real-time monitoring while tracking efficiency, features, failures and weaknesses from a single cell up to the whole infrastructure. Thus, the decision-making process is simplified, which contributes to reducing failures, wastes and, consequently, costs.

A double-closed loop DC/DC converter based on a piezoelectric transformer

Nowadays, piezoelectric transformers (PT) are a good alternative to substitute magnetic materials in AC/DC and DC/DC converters. They have high isolation voltage and operate at high frequencies, with lower losses. However, their optimum operating frequency exhibits a strong dependence on different parameters, such as temperature, load or voltage level applied. This usually causes an inconvenience, because this drift affects PT gain and efficiency, which can vary enormously within a few hundred of hertzs. On the other hand, it is not only necessary to ensure the PT is driven at the proper frequency -in terms of gain and efficiency, including zero voltage switching (ZVS) in the power stage- but also to regulate the output voltage. In this paper, two simple feedback loops are implemented in a PT based DC/DC converter: One of them adjusts the switching frequency to obtain the best gain and efficiency. The other performs the output voltage regulation.

High power density DC/DC converter using thick-film hybrid technology

The tendency to push down supply voltages (3.3 V, 2.7 V...) in telecommunication equipment makes DC/DC conversion systems be placed as close as possible to the load, thus minimizing losses due to high currents. Size is a critical feature in these supply systems, with passive components usually being the bulkiest elements. A 10 watt DC/DC converter is presented in this paper where passive components have been integrated using hybrid technology, thus allowing to obtain high power density of 6.25 W/cm/sup 3/.

A quick way to determine the optimum layer size and their disposition in magnetic structures

Designers of high-frequency magnetic elements (transformers) in switch mode power supplies (SMPS) lack of appropriate methods to select the optimum winding strategy and conductor size. This paper presents an approximate method to carry out this selection in a quick and easy way. The way to use it and the results obtained are also included.