João B. Vieira

Front-End Converter With Integrated PFC and DC–DC Functions for a Fuel Cell UPS With DSP-Based Control

This paper presents the development of a boost converter with integrated power factor correction (PFC) and dc-dc functions for a proton exchange membrane fuel cell (PEMFC) uninterruptable power supply (UPS). Through the use of a passive resonant soft-commutation cell, which besides providing improvements in efficiency and reduced electromagnetic interference, produces a naturally controlled supercapacitor charger circuit. Supercapacitors are employed in order to provide a proper startup of the PEMFC and to improve its dynamic response. The control strategy is implemented using a digital signal processor and is based on the average current control method for sinusoidal input current imposition ensuring, therefore, a high input power factor and low harmonic distortion of current. The main features of the proposed solution are the use of a PEMFC as an energy storage system, which replace the battery banks commonly used in UPS systems, eliminating the common drawbacks related to working life and maintenance issues, and the use of a front-end converter with integrated PFC and dc-dc functions eliminating the necessity of using an additional and dedicated dc-dc converter for the PEMFC. During power failure or even in conditions of severe voltage sags on the ac mains, the PEMFC is activated assuring the continuous power supply to the electronic load connected to the dc link. In this paper, the authors present the full study description including experimental results that corroborate with the theory herein presented.

A comparative study of irradiation systems for photoinactivation of microorganisms

The construction of LED systems applied to photosensitization processes was studied. Aiming to obtain more efficient devices it was evaluated the use of high intensity LED (HPLED), that present greater photonic flux, tending to excite a greater fraction of molecules. Construction details for 3 different irradiation systems were described (filtered halogen bulbs, conventional LED, HPLED), using methylene blue as a photosensitizer. A comparison between the efficiency of the equipments was carried out through the kinetics of photooxidation of 1,3-Diphenylisobenzofuran and Staphylococcus aureus photoinactivation. The overlap between the light emited from each equipment and the photosensitizer absorption, was also an important parameter in estimating the efficiency of the equipment. Bacterial inhibition higher than 99% for concentrations of 5 × 10-6 mol dm-3 of the photosensitizer was observed, in the system that uses HPLED. The equipments based on LED showed satisfactory results, besides their low cost and simple to assembling.

Current-sensorless PFC Boost converter with preprogrammed control strategy

The development of front-end converters for power factor correction and DC link voltage control of power electronics converters such as, UPS, Inverters, and Switched Power Supplies, has been attracting great interest from the scientific community that works toward the achievements of cost reduction, high efficiency, and reliability. In this context, this paper proposes an innovative microprocessed control technique for sinusoidal input line current imposition in front-end sensorless Boost converters, named in this work as PFC-BOOST-CSL. The proposed method is based on experimental acquisition of gate-drive signal sequences for different load conditions. These signals correspond to a complete cycle of the AC input voltage and are recorded in the microcontroller memory in order to be reproduced when used in a Boost converter without current sensor. In the operation of PFC-BOOST-CSL, a suitable switching sequence is sent to drive the power switch in order to minimize output voltage error and maintain a sinusoidal input current. Aiming to prove the proposed digital control concept, a 600W PFC-BOOST-CSL prototype was built and analyzed in laboratory and the main experimental results are presented herein.

Class D power amplifier used as an electronic ballast

This paper presents a class D power amplifier used as an electronic ballast topology that can be used to supply one or more high pressure sodium lamps. It is ideal for poles luminaries with one or more High Pressure Sodium lamps used in private or public lighting. The proposed ballast supplies the lamps using synthesized waveform with fundamental frequency below 1 kHz in order to avoid acoustic resonance and minimize luminous flux oscillation. Control strategy, design guide line and experimental results are also included in this paper proposal.

A Non-Insulated Step-Up/Down DC-DC Converter with Wide Range Conversion

In this paper an approach of a step-up/down dc-dc converter with wide range conversion called Boost2-Buck is presented. The proposed converter presents nonpulsating input and output current. It has operations equivalent to a cascade converter consisting of two boost converter and one buck converter, but with the advantage of using single active switch. Mathematical analysis and experimental results are presented for converter operating with output power of 20W.

Hybrid three-phase rectifier with high power factor and voltage sags ride-through capability for utility inteface of adjustable speed drives

Temporary voltage sags are the main cause of untimely arrest in automated systems that use adjustable speed drives (ASDs). In this context, this paper presents an analysis of a new hybrid three-phase rectifier designed to correct the power factor and to promote voltage sag ride-through capability to ASDs. To prove the effectiveness of the proposed solution, this paper presents results of simulations for several case studies, evaluating the performance of the proposed hybrid rectifier before the voltage sags types A, B, C, D, E, F and G. In all cases under analysis, it was proved that the proposed solution is effective and very attractive for applications in high power. Experimental results under normal power supply for an output power of 5 kW are presented.

Turn-on turn-off zero-current-switching converter in power factor correction (PFC) application

This paper presents a turn-on turn-off zero-current-switching (ZCS) converter in a PFC boost application. The applied soft-commutation cell is capable of providing ZCS operation keeping the main switch current equal to the input current. Substituting the typical PWM cell found in classics power converter structures by the presented ZCS cell with three switches and taking to account the invariance principle, zero current switching of all active switches is achieved without additional current stress of the main switch. The operation and main properties of this converter are also included. Design guidelines with a design example are described and verified by simulation results.

Hybrid high-power rectifier with reduced THDI and voltage sag ride-through capability

Temporary voltage sags are the main cause of untimely arrest in automated systems that use adjustable speed drives (ASDs). In this context, this paper presents an analysis of a new hybrid three-phase rectifier designed to correct the power factor and to promote voltage sag ride-through capability to ASDs. To prove the effectiveness of the proposed solution, this paper presents results of simulations for several case studies, evaluating the performance of the proposed hybrid rectifier under the voltage sags types A, B, C, and D. In all cases under analysis, it was proved that the proposed solution is effective and very attractive for retrofitting applications in high power.

DSP-based implementation of input line current imposition strategy for a single-phase hybrid rectifier

Due to the considerable increase of electronic power processing devices in various segments of industry it becomes necessary to control and limit the current harmonic content injected into the distribution systems through the development of pre-regulator converters. In this context, this paper presents the development and experimental analysis of a new structure of single-phase hybrid rectifier with high power factor and low harmonic distortion of current and digital control based on DSP (Digital Signal Processor). In this proposed hybrid rectifier structure the switched converter process reduced portion of active power delivered to the load and therefore the overall efficiency of the structure is increased. The PWM control technique implemented is able to limit the contribution of the switched converter and at the same time impose an input AC current whose harmonic spectrum is in accordance with the limits imposed by the international standard IEC61000-3-2. Mathematical modeling and experimental results are presented corroborating with the theoretical analysis also included.

Conversor boost atuando como carga eletrônica a corrente controlada para fins de teste de uma célula a combustível

This paper presents the study and implementation of an electronic load for fuel cell testing. In a typical fuel cell electrical testing, it is necessary to draw a controllable dc current from it, thus an electronic load based on the boost converter is connected to the cell to control its output current. The design procedure and simulation results are presented. In order to validate the design method and verification of the effectiveness of the converter in this application, experimental results are also presented.