Henrique A. C. Braga

Boost current multilevel inverter and its application on single-phase grid-connected photovoltaic systems

This work presents a novel current multilevel (CML) inverter topology, named boost CML inverter, and its application on energy processing of single-phase grid-connected photovoltaic (PV) systems. The structure allows a high power factor operation of a PV system, injecting a quasi-sinusoidal current into the grid, with virtually no displacement in relation to the line voltage at the point of common coupling among the PV system and the loads. The major appeals of using the CML technique are the balanced current sharing among semiconductor switches and the decrease of the current slope in the circuit devices, with a consequent reduction of conducted and radiated electromagnetic interference (EMI). The CML technique also allows adapting or minimizing current waveforms harmonic content. System description, mathematical approach, and design guidelines are presented, providing an overview of the new topology. In order to validate the proposed concepts, experimental measurements, made in a small-scale laboratory prototype, are also presented. The obtained results evidence the feasibility of the application of this new topology on singlephase grid-connected PV systems.

Application of a generalized current multilevel cell to current-source inverters

In this paper, a new cell which lends itself as a generic current multilevel one is applied to current-source inverters with output current harmonics minimization and without the use of high-frequency modulation. In this cell, inductors acting as current sources ensure equal current division among switches. DC current balance in the inductors is achieved, also, without closed-loop control. It is also shown that, while, for the five-level structure it is easy to find a proper control strategy, for higher levels, it is necessary to use numerical simulation programs to find out a proper switching strategy. Simulation and experimental results are included to show the performance of the new cell for high-power applications.

A 3-kW unity-power-factor rectifier based on a two-cell boost converter using a new parallel-connection technique

This paper applies a parallel-connection technique to a boost converter with power factor correction. By means of a small extra inductance two MOSFET-PWM cells are associated in parallel, leading to an improved performance and reliable switched converter, along with simplified layout requirements. A comparison of the structure used in this paper with some alternative techniques is also provided. A simplified mathematical analysis of the main circuit, based on the PWM-switch model, is also presented along with digital simulation results. Results from a 3 kW-70 kHz prototype operating with power-factor correction (PFC) and soft commutation show that the technique is very useful. It is capable of reducing diode reverse-recovery problems, increasing the efficiency of the converter and also improving the overall reliability.

Matching LED and Driver Life Spans: A Review of Different Techniques

A review of various proposed schemes to increase the reliability and life span of solid-state lighting (SSL) systems is presented in this article. Since the mainstream devices employed for such lighting systems are inorganic, high-power light-emitting diodes (LEDs), which are devices characterized by their very long life, most of the questions in reliability and endurability arise from the electronic offline circuit driving the LEDs. Issues regarding the limited reliability of specific components, such as electrolytic capacitors, are introduced. Several power-?conversion configurations aimed to capacitance reduction and capacitor technology exchange are put forward as alternative solutions for implementing long-life drivers, with remarks on both their benefits and drawbacks. An extensive literature review on the topic is carried out, and some practical outcomes from recent research on offline LED driving are highlighted.

Integrated SEPIC buck-boost converter as an off-line LED driver without electrolytic capacitors

In this work, a new topology of integrated converter is proposed to be used as an off-line LED driver. The two stages of the converter are made up by a front-end SEPIC power factor corrector and a buck-boost converter for current regulation, both stages sharing the same power switch. It is demonstrated that when both stages work in DCM, less low-frequency ripple is transmitted from the bus capacitor to the output, allowing decreasing the amount of filtering needed and eliminating electrolytic capacitors from the power circuitry. Photometric data is used to size the maximum current ripple permissible at the LEDs, further optimizing filtering requirements and reducing capacitances to the maximum.

Offline Soft-Switched LED Driver Based on an Integrated Bridgeless Boost–Asymmetrical Half-Bridge Converter

This paper proposes an offline single-stage light-emitting diode (LED) driver based on a novel approach to reduce low-frequency ripple in LED arrays supplied from mains, while assuring high input power factor (PF). The proposal employs a series resonant dc-dc converter integrated into a bridgeless boost power factor correction (PFC) stage. The resonant stage works to reduce the low-frequency ripple transmitted from the output of the PFC stage to the LEDs with only small power losses. This solution achieves three main goals: 1) reduction of the bulk capacitance used at the dc bus, allowing for the use of long-life film capacitors; 2) increase in the overall efficiency of the LED driver owing to the low switching and conduction losses in the shared switching network; and 3) assuring high input PF. Experimental results of a driver without electrolytic capacitors for a 100-W street lighting LED luminaire are presented, showing overall efficiency in excess of 92%, input PF greater than 0.97, and line current harmonic content in compliance with the IEC 61000-3-2 standard.

Analysis of voltage droop control method for dc microgrids with Simulink: Modelling and simulation

This work presents a performance study of a dc microgrid when it is used a voltage droop technique to regulated the grid voltage and to control the load sharing between different sources. A small model of a dc microgrid comprising microsources and loads was implemented in the Simulink/Matlab environment. Some aspects about centralized (master-slave) and descentralized (voltage droop) control strategies as well as the procedures to design the controllers, with and without droop control, are presented and discussed. Simulation results obtained with the digital model of the dc microgrid with three microsources will be presented to validate the effectiveness of the voltage droop strategy, applied to proportional and proportional-integral controllers, to regulate the microgrid voltage.

An experimental comparison between different technologies arising for public lighting: LED luminaires replacing high pressure sodium lamps

This work deals with the analysis and photometric comparison between different systems concepts for public lighting, hence the solid state lighting (SSL) employing LED luminaires with electronic drivers and the conventional high pressure sodium (HPS) lamp based luminaires along with electromagnetic ballasts. The study and comparison raise question on the relative perception of the human eye to different light sources with different spectral distributions, devoting special attention to low luminance conditions (scotopic) such as those present on public roadway lighting. Different LED-based luminaires are tested, in the lab and in loco. Photometric data of a SSL system being currently installed for the replacement of current HPS luminaires at the School of Engineering of the Federal University of Juiz de Fora are provided for the analysis and comparison.

An experimental study on the photometrical impacts of several current waveforms on power white LEDs

Since light-emitting diodes (LEDs) are a rising lighting technology, a great amount of research is currently being focused on driving techniques for these current-fed semiconductor devices. For realizing efficient current drivers, power electronics is usually employed. This work focuses on studying the impacts that several high and low frequency current waveforms commonly found on power electronic drivers may have on the photometrical and colorimetrical performance of the LEDs themselves. Empirical evidence obtained under controlled experiments is provided to correlate important features of the LEDs to the current levels and waveforms.

Application of a generalized current multilevel cell to a current source inverter

In this work, a new cell which lends itself as a generic current multilevel system is applied to a five level current source inverter (CSI) with output current harmonics minimization and without the use of high frequency modulation. In this cell, inductors acting as current sources ensure equal current division among switches. DC current balance in the inductors is also achieved without closed-loop control. Two switching strategies are used to demonstrate the performance of the cell. The first switching strategy is known as a symmetric strategy. A second, known as an asymmetric strategy is suggested by the authors. A comparison between the two strategies is also made. Simulation and experimental results are included to show the performance of the new cell in a current source inverter for high power applications.