F.F. Linera

Design of a Soft-Switching Asymmetrical Half-Bridge Converter as Second Stage of an LED Driver for Street Lighting Application

High-brightness LEDs are considered remarkable lighting devices due to their high reliability, chromatic variety, and increasing efficiency. As a result, a high number of solutions for supplying LED strings are emerging. One-stage solutions are cost-effective, but their efficiency is low because they have to fulfill several purposes with only one converter: power factor correction (PFC), galvanic isolation (in some cases), and current regulation. Two-stage and three-stage solutions have higher efficiency because each stage is optimized for only one or two tasks and they are the preferred options when supplying several strings at the same time. In this paper, a two-stage solution is proposed. The first stage is the well-known PFC boost converter. The second stage, on which this paper is focused, is the asymmetrical half bridge (AHB). Its design has been optimized based on the needs and characteristics of LED-based street lighting applications. The proposed transformer design (with asymmetrical secondary windings) minimizes the conduction losses while the model of the converter during the dead times optimizes their duration, reducing switching losses in the MOSFETs and diodes. Experimental results obtained with a 40-W prototype show an efficiency as high as 94.5% for this second stage and validate the proposed design procedure and model.

Intelligent and universal fast charger for Ni-Cd and Ni-MH batteries in portable applications

In this paper, a new fast charger is presented for Ni-Cd and Ni-MH batteries, which are the most frequently used in portable applications. In this charger, the control and supervision of the process has been entrusted to a microcontroller, which provides a powerful and intelligent tool to undertake complex tasks, and reduces the requested circuitry to the microcontroller itself and a few additional components. The resulting charger is able to work out the initial battery state (detecting deteriorated devices), decide the suitable way to charge it (ensuring a long cyclic life), and determine when the charge process must be finished. This way, the state of the battery is always controlled, preventing any damage to it and providing a fully protected operation mode. This paper summarizes the design and construction of the presented charger, as well as shows the experimental results obtained in the prototype tests.

A new full-protected control mode to drive piezoelectric transformers in DC-DC converters

Due to their high power density and their low EMI generation, piezoelectric transformers (PTs) are an attractive solution to replace magnetic transformers in AC/DC power converters. However, this substitution implies changes in the power topology and the control strategy because of the very frequency-dependent behavior of PTs, and their capacitive features. In previous works, some power topologies have been presented to deal with this new component, and frequency modulation has been assumed as the natural way to control the output voltage, sometimes in combination with pulse width modulation (PWM), to achieve both line and load regulation. In the frame of a particular application, this paper presents a new control method for PT-based converters. This control method is very simple to design, requires very few components and regulates the output voltage maintaining constant the frequency and the pulse width, trying to obtain the best characteristics from the piezoelectric device.

A modular PV regulator based on microcontroller with maximum power point tracking

We can find many different types of commercial regulators in the market, these devices basically can be divided into two categories according to their operation mode: The first ones modulate the input voltage with PWM (pulse width modulation) to hold the constant voltage in the output necessary to charge the battery. The other ones operate in the MPP (maximum power point) of the PV (photovoltaic) array, tracking it by different ways depending on the type of regulator; these regulators are called MPPTs (maximum power point trackers). The increase of power using a maximum power point tracker can be up to 25%. This paper presents a regulator which can operate in the maximum power point of PV arrays regardless of the meteorological conditions and the effects of them in the dispersion of the PV array characteristics. Parallel connection of this kind of regulators is also proposed, which allows installation without the need to get rid of previous equipment.

Small-Signal and Large-Signal Analysis of the Two-Transformer Asymmetrical Half-Bridge Converter Operating in Continuous Conduction Mode

The asymmetrical half-bridge converter (AHBC) has many advantages over other PWM converters. The possibility of soft switching in primary switches and reduced switching losses in the secondary ones implies that the AHBC is a suitable topology for many high-performance applications. Besides, the lack of dead times, except those needed for achieving soft switching, is a very interesting feature to implement self-driven synchronous rectification. Moreover, the small size of its output filter is also a remarkable advantage in some fields (e.g., LED lighting). On the other hand, it also has some disadvantages. One of them is the short range of the duty cycle (lower than 0.5) and the other one is the difficult regulation due to a complex transfer function. The two-transformer AHBC (TTAHBC) solves the first problem as it enlarges the duty cycle range making its top limit higher than 0.5. Nevertheless, the regulation of this converter is still very complex and, besides, the transfer functions of the standard AHBC are not valid for the TTAHBC. As a consequence, the small- and large-signal models have yet to be studied. In this paper, the complete small-signal and large-signal analysis of the TTAHBC operating in continuous conduction mode is provided. The large-signal and small-signal models are developed taking into account the main parasitic components that affect the transient response of this converter. The validation of the resulting model is carried out by means of both, simulation and experimental results. The prototype is a 60-W TTAHBC designed for an input voltage of 400 V and an output voltage of 48 V.

Tutoring System for the Efficient Driving of Combustion Vehicles

One of the sectors that currently generates pollution is road transport. Every day, millions of tons of CO2 are released into the atmosphere because of this type of human activity. Governments see the reduction of such emissions as a priority-which, according to various studies, could be achieved through more efficient driving. This paper presents a driver tutoring system based on active learning and ubiquity paradigms. Through visual and auditory recommendations, we are able to help drivers achieve more efficient driving. This system is complemented with a Web portal where drivers can check their driving and receive recommendations for further improvement. To evaluate the performance of the tutoring system, driving is monitored and analyzed over a period of six weeks with 150 volunteer drivers achieving results that improved efficient driving metrics and consumption by ~ 10%.

Flatten it out

Measuring the flatness of a cold-rolled steel strip or aluminum foil is a vital aspect of production quality control. Cold lamination control based on the results of this measurement crucially affects production efficiency, but further processes can modify flatness, which can be lost when the strip becomes cold. We describe a low-cost flatness measurement system to monitor this property at several production line points. The system is composed of a capacitive sensor array, some microcontrollers, and a PC for computing and visualization. Measurements on a production line are provided and analyzed.

A new speed measurement system

Magnetic contactless speed measurement sensor targets steel industry. Controlling any production line requires the use of many sensors along the line. A basic measurement in steel lines is the determination of the exact linear speed of some portions of the process. This article comments on the complete speed measurement system for steel lines, with a cost lower than US

Practical Speed and Elongation Measurement, Using Encoders, for a Temper Mill

300, a range up to 800 m/min, and accuracy of about 0.4%. Accuracy is influenced by the position of the sensors.

Practical speed and elongation measurement, using encoders, for a Temper mill

Speed and differential speed measurements are necessary for almost all of manufacturing steel processes. Use of incremental rotary encoder is the cheapest method for this purpose. Classical theoretical algorithms are analyzed in terms of error and sampling time. These methods are used for a temper mill real case, showing the practical limitations in both speed and differential speed. A new differential speed measurement algorithm is introduced, showing how to solve eccentricity problems and that a bad processing but not slippage is the source of observed false elongation peaks. Thus, incremental rotary encoder with a proper processing algorithm can offer higher accuracy than other more expensive noncontact speed sensors.