Controladores LED eficientes para aplicações de iluminação geral

摘要

The ever growing energy consumption trends and its impact on the environment has triggered worldwide attention. This has motivated several measures, such as the Kyoto protocol, or the 20 20 20 European strategy, aiming at the reduction of energy consumption. Globally, these measures defend a better and efficient usage of the available energy. This in turn is strongly linked to public awareness and the introduction of efficient electronic equipment. Public street lighting is a good example of these trends, where both aspects are of the utmost importance. The introduction of power LEDs as future lighting devices has motivated several advances coping with these strategies. On one side, LEDs are able to deliver higher efficiency when compared to conventional lighting devices. This has triggered the replacement of old style luminaires by LED based ones. However, their high cost has prevented full adoption and at the present stage, is acting as a slowing down force against this replacement trend. Better solutions are under research on the framework of several European projects.Power LEDs are solid-state devices able to support fast switching, a feature which was not fully supported by conventional lighting devices. Combining this feature with environmental sensing and intelligent control may lead to better power savings. A simple approach would be to consider the that the actual lighting demands depend on the street usage and surrounding lighting levels. For this purpose, the combination of twilight sensors, motion detectors and intelligent control schemes may provide a suitable approach. This way, the real lighting demands can be effectively taken into consideration, providing luminaires able to consume the least possible energy. For this to become a reality several challenges have to be addressed. One of the most important challenges is the LED driver design.Modern lighting systems based on LEDs, replace the traditional ballasts by LED drivers. When efficiency is a major concern, such as in public street lighting, these drivers have to be designed in order to be the most robust and efficient as possible. Recurring solutions resort to switched mode power supplies, able to support light dimming. One of the major problems with these drivers is the fact that their efficiency decreases for lower dimming levels. This is of the utmost importance for public street lighting, as most of the time during night, the luminaires are on a low lighting level (as changes to high lighting conditions depend on street usage). Thus, in order to promote better power savings, the efficiency of the driver should be high for both lighting conditions. Commercially available drivers, exhibit efficiencies on the 90% range for the high lighting conditions, with only 40% to 60% under the low lighting. On the framework of this master dissertation it was investigated the problem of LED driver design aiming at the highest possible uniformity of the efficiency curve, under different loading and dimming conditions. The selected approach was based on quasi-resonant flyback converter, backed up by an active power factor correcting block. The designed driver supports remote configuration and monitoring as well as sensor integration. The archived results show that this driver achieves a peak efficiency of 93% under maximum load and 100% duty-cycle. The efficiency for low dimming conditions (10% duty-cycle) achieves 75%.