William Dotto Vizzotto

Design Methodology for Light-Emitting Diode Systems by Considering an Electrothermal Model

The knowledge about thermal, electrical, and photometrical characteristics of Light-Emitting Diodes (LEDs) is essential to achieve a good performance to the lighting system. This paper presents a methodology for designing LED systems. The main purpose is to provide an optimal operating point, considering the electrothermal design to achieve the maximum luminous flux for a given LED system. Based on two design routines, the proposed methodology brings the possibility to consider driver output current, heatsink size, and LED junction temperature in the system design. A mathematical analysis taking into account an LED electrothermal model is presented. Computational fluid dynamics simulation employing finite element method and experimental results validate the proposed methodology.

Bidirectional Grid-Tie Flyback Converter Applied to Distributed Power Generation and Street Lighting Integrated System

This paper presents a multifunctional bidirectional converter applied to street lighting and photovoltaic (PV) microgeneration systems. The proposed converter works as an electronic driver supplying a street lighting luminaire based on light emitting diodes (LEDs) at night, from ac single-phase mains with high power factor and reduced harmonic distortion. During daylight hours, the converter injects the produced energy by a PV panel to the grid, working as a grid-tie inverter. The proposed topology is based on the integration of two flyback converters, one for each half-cycle of the grid voltage, avoiding the usual diode bridge rectifier for LED lamps drives, thus providing a bidirectional power flow. A prototype of the proposed electronic stage has been designed, built, and tested, in order to validate the system. Finally, experimental results are presented. In rectifier mode, an efficiency of 86% was achieved, whereas an efficiency of 89% was obtained in inverter mode.

Indirect control of luminous flux and chromatic shift methodology applied to RGB LEDs

This paper presents a method of control for RGB LED systems, modelling and equating of a system of LEDs are shown in details in order to obtain constant output luminous flux information for each color, reducing the color shift with the temperature variation. Also the paper discusses the control strategy employed and the methodology employed to eliminate the temperature influence on the color shift. Some simulation results are shown in order to prove the methodology, followed by some practical results.

Hybrid system of distributed power generation and street lighting based on LEDs: Grid connection

This work proposes an electronic driver for street lighting systems integrated to renewable energy. In recent lighting applications, the use of micro renewable generators in lighting points makes necessary the use of special electronics to handle the bidirectional energy flow in the ballast. The proposed input stage is a topology based on the integration of two flyback converters with different polarities, in order to avoid the use of the input diode bridge rectifying stage, allowing the converter operate with bidirectional energy flow. Thus, this system has two distinct operation modes. The rectifier mode is responsible to supply a street lighting system based on LEDs from de utility grid during the night, and the inverter mode must deliver energy into the power grid provided by a solar panel during the day. This work focuses in the inverter stage, which comprises a boost converter, responsible for the Maximum Power Point Tracking (MPPT), and a flyback inverter. The present topology is an alternative to standard bidirectional input stages, as it can be used to deliver energy into the power grid, due the avoidance of the input diode bridge.

Electrothermal characterization applied to the study of chromaticity coordinates in RGB LEDs

The purpose of this paper is the development of a methodology to analyze the chromaticity coordinates in RGB LEDs, considering the influence of junction temperature. A review of theoretical concepts of colorimetry was performed, as well as a demonstration of the luminous flux equation that considers the effect of thermal and electrical characteristics of LEDs. The equations which represent the heatsink and junction temperature of the LEDs are compared with finite element simulations and experimental measurements. The equation of the luminous flux is related to the matrices of the tristimulus, to achieve a precise relationship between the LEDs operation condition and the desired color. Finally, tests in order to verify the data mathematically obtained in comparison with the data experimentally obtained are performed and shown.

Design space for LED systems considering photoelectrothermal aspects

The knowledge of the interrelationships among the photometrical, electrical and thermal (photoelectrothermal) parameters is extremely important to design lighting systems based on light-emitting diodes (LEDs). This paper proposes a novel methodology based on the luminous flux estimation of LEDs considering a photoelectrothermal design space. The main contribution of the proposed methodology is the use of only LED datasheet information, which avoids experimental tests to obtain the LED data. This methodology provides 3D and 2D space designs, which helps to identify the luminous efficacy, heatsink thermal resistance and junction temperature of the system without requiring experimental tests or simulations with high computational cost. Thus, the designer can define the minimum system requirements and design the system with emphasis in the desired features. The proposed design methodology has been verified experimentally using three different scenarios, presenting satisfactory results.

An optimized methodology for led lighting system designers: A photometric analysis

This paper presents a study about photometric performance of LEDs (light-emitting diodes) using an optimized methodology for LED lighting systems. The objective is to evaluate and quantify the flicker produced in LEDs supplied with current ripples commonly found in LED drivers. An optimal point of operation is approached taking into account thermal, electric and optical LED system characteristics. The results are compared with levels of perception and acceptability previously presented in the literature.