Using an LED as a sensor and visible light communication device in a smart illumination system

The need for more efficient illumination systems has led to the proliferation of Solid-State Lighting (SSL) systems, which offer optimized power consumption. SSL systems are comprised of LED devices which are intrinsically fast devices and permit very fast light modulation. This, along with the congestion of the radio frequency spectrum has paved the path for the emergence of Visible Light Communication (VLC) systems. VLC uses free space to convey information by using light modulation. Notwithstanding, as VLC systems proliferate and cost competitiveness ensues, there are two important aspects to be considered. State-of-the-art VLC implementations use power demanding PAs, and thus it is important to investigate if regular, existent Switched-Mode Power Supply (SMPS) circuits can be adapted for VLC use. A 28 W buck regulator was implemented using a off-the-shelf LED Driver integrated circuit, using both series and parallel dimming techniques. Results show that optical clock frequencies up to 500 kHz are achievable without any major modification besides adequate component sizing. The use of an LED as a sensor was investigated, in a short-range, low-data-rate perspective. Results show successful communication in an LED-to-LED configuration, with enhanced range when using LED strings as sensors. Besides, LEDs present spectral selective sensitivity, which makes them good contenders for a multi-colour LED-to-LED system, such as in the use of RGB displays and lamps. Ultimately, the present work shows evidence that LEDs can be used as a dual-purpose device, enabling not only illumination, but also bi-directional data communication

Power Efficient VLC Transmitter Based on Pulse-Width Modulated DC-DC Converters and the Split of the Power

Visible Light Communication (VLC) has gained relevance during the last years. It consists in using High-Brightness LEDs (HB-LEDs) both for lighting and for transmitting information changing the light intensity rapidly. However, there are some bottlenecks that are slowing down the deployment of this technology. One of the most important problems is that the HB-LED drivers proposed for addressing high data rates in VLC achieve poor power efficiency. Since these HB-LED drivers must be able to reproduce fast current waveforms, the use of Linear Power Amplifiers (LPAs) has been adopted, which clearly damages the power efficiency of HB-LED lighting. In order to alleviate this problem, a HB-LED driver made up of two DC-DC power converters is presented in this work. One of them is responsible for performing the communication functionality by operating at high switching frequency (10 MHz), whereas the second converter fulfills the illumination functionality by ensuring a certain biasing point. The split of the power allows us to minimize the power delivered by the fast-response DC-DC power converter, which suffers from high switching losses. Thus, the overall efficiency can be maximized for each particular communication scenario and for scenarios with changing condition

Design and implementation of a bi-directional visible light communication testbed

Abstract. This work defines a bi-directional visible light communication (VLC) testbed design and implementation process using Universal Software Radio Peripheral (USRP) software defined radios (SDR) and open-source software. The visible light communication design uses LED light sources for wireless communications purposes. The testbed combines light, infrared and radio frequencies as wireless media to be utilized in a hybrid wireless communication system. Bi-directional communication at 12.5 Mbps bit rate was successfully achieved and only limited by a sample rate of the USRP system. The achieved communication distance was in the range of 0.5 to 7 meters depending on the used optics. A TCP-IP communication and access to the Internet was also established by using light and infrared communication links. The Internet connection was also established by using power line communication for providing data to the lighting through the existing power line cables. The results in the work were obtained by using a GMSK modulation. Also, GFSK, QPSK, 8-PSK, 16-QAM and OFDM modulation were initially tested for future study.Kaksisuuntaisen näkyvän valon tiedonsiirtotestialustan suunnittelu ja toteutus. Tiivistelmä. Työssä suunnitellaan ja rakennetaan kaksisuuntainen kokeiluympäristö valon käyttöön langattomassa tiedonsiirrossa käyttäen ohjelmistoradioita ja avoimen lähdekoodin ohjelmistoja. Kokeiluympäristössä voidaan tutkia ja käyttää valon, Infrapunan ja radioaaltojen taajuusalueita tiedonsiirtoon. Valon tiedonsiirrossa käytetään valaistuskäyttöön suunniteltuja LED valaisimia sekä valaistukseen että tiedonsiirtoon. Työssä saavuttiin laitteiston näytteistystaajuuden rajoittama kaksisuuntainen 12,5 Mb/s tiedonsiirtonopeus ja käytetyn optiikan ominaisuuksista sekä tiedonsiirtonopeudesta riippuvainen tiedonsiirtoetäisyys 0,5–7 metriä. Järjestelmään ohjelmoitiin valo- ja infrapunalinkin avulla toimiva TCP-IP yhteys Internetiin. Internet yhteys valaisimelle onnistuttiin siirtämään myös käyttäen sähköverkon valmiita kaapelointeja. Työn tulokset saavuttiin käyttäen GMSK moduloitua signaalia. Myös GFSK, QPSK, 8-PSK, 16-QAM ja OFDM modulaatioiden toimivuus testattiin tutkimuksen jatkoa varten

Controladores LED eficientes para aplicações de iluminação geral

Mestrado em Engenharia Eletrónica e TelecomunicaçõesThe 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%.As tendências de consumo de energia cada vez maior e seu impacto sobre o meio ambiente tem captado a atenção a nível mundial. Isso tem motivado várias medidas, tais como o Protocolo de Quioto, ou a estratégia Europeia 20 20 20, visando a redução do consumo de energia. Globalmente, estas medidas defendem um uso melhor e eficiente da energia disponível. Este, por sua vez, está fortemente ligado à consciência pública e à introdução de equipamento eletrónico eficiente. A iluminação pública é um bom exemplo dessas tendências, em que ambos os aspetos são de extrema importância. A introdução de LEDs como dispositivos de iluminação tem motivado vários avanços que lidam com essas estratégias. De um lado, os LEDs são capazes de oferecer uma maior eficiência quando comparados com dispositivos de iluminação convencionais. Isso provocou a substituição de luminárias convencionais por luminárias baseadas em LED. No entanto, o custo elevado destes dispositivos tem impedido a adoção plena e na fase atual, está mesmo a atuar como uma força negativa contra esta tendência de substituição. Melhores soluções estão sob investigação no âmbito de vários projetos europeus. Os LEDs são dispositivos de estado sólido, capazes de suportar a comutação rápida, uma característica que não é totalmente suportada por dispositivos de iluminação convencionais. Combinando esta característica com sensores ambientais e controlo inteligente pode-se ambicionar melhores poupanças energéticas. Uma abordagem simples seria a de considerar o que as exigências de iluminação reais dependem do uso das ruas e os níveis de iluminação circundantes. Para este efeito, a combinação de sensores de crepúsculo, detetores de movimento e regimes de controlo inteligentes podem propiciar uma abordagem adequada. Desta forma, os requisitos reais de iluminação podem ser efetivamente considerados, fornecendo luminárias capazes de consumir apenas a energia necessária. Para que isto se torne uma realidade vários desafios têm de ser vencidos. Um dos desafios mais importantes é o projeto LED driver. Nos sistemas de iluminação modernos baseados em LEDs, substitui-se os balastros convencionais por LED drivers. Quando a eficiência é importante, como no caso da iluminação pública, O LED driver têm de ser concebido de forma a ser o mais robusto e eficiente possível. Soluções recorrentes usam a fontes de alimentação comutadas, capazes de suportar o escurecimento adaptativo do fluxo luminoso. Um dos problemas principais no projeto destes drivers é o facto de a sua eficiência diminuir para níveis de regulação mais baixos. Isto é de extrema importância para a iluminação pública, pois na maioria dos casos durante a noite, as luminárias estão num nível de iluminação de baixo. Assim, com a finalidade de promover uma melhor economia de energia, a eficiência do driver deve ser elevada para ambas as condições de iluminação. Drivers comercialmente disponíveis, exibem eficácias na gama de 90% com elevado fluxo luminoso, e apenas 40% a 60% na condição de baixo fluxo luminoso. No âmbito desta dissertação de mestrado foi investigado o problema do projeto de driver LED visando a maior uniformidade possível da curva de eficiência, sob diferentes condições de carga e de fluxo luminoso. A abordagem escolhida foi baseada no conversor flyback quasi-ressonante, apoiado por um bloco de correção de fator de potência ativa. O driver projetado suporta configuração e monitorização remota, bem como de integração de sensores. Os resultados alcançados mostram que este driver atinge um pico de eficiência de 93% na condição de carga máxima e máximo fluxo luminoso. A eficiência em condições de baixo fluxo luminoso é superior a 75%

Power-Efficient VLC Transmitter Able to Reproduce Multi-Carrier Modulation Schemes by Using the Output Voltage Ripple of the HB-LED Driver

2018 IEEE 19th Workshop on Control and Modeling for Power Electronics (COMPEL), 25-28 junio, Padua (Italia)Visible Light Communication (VLC) consists in using High-Brightness LEDs (HB-LEDs) not only for lighting, but also for transmitting information by changing the light intensity rapidly. One of the most important problems of VLC is that the HB-LED drivers that have been proposed for achieving the highest bit rates offer low power efficiency. The reason is that since these HB-LED drivers must be able to reproduce fast current waveforms, the use of Linear Power Amplifiers (LPAs) has been adopted, which damages the power efficiency of HB-LED lighting. To the author’s knowledge, there is only one approach reported in the literature that is able to reproduce the most recommended modulation schemes by using a power efficient HB-LED driver. However, since it is based on the use of pulse-width modulated dc-dc power converters, the required switching frequency is between 3 and 6 times higher than the maximum frequency of the communication signal. As a result, the approach suffers from high switching losses when the highest bandwidths are addressed. A method for reproducing the most recommended modulation schemes by modulating both the amplitude and the phase of the output voltage ripple is presented in this work. The major benefits are the high efficiency, the simplicity and the lower switching frequency required for the implementatio

A Family of High Frequency AC-LED Drivers Based on ZCS-QRCs

A family of dimmable AC-LED drivers fed from dc voltages, is presented in this paper based on Zero Current Switching Quasi-Resonant Converters (ZCS-QRCs). The proposed family of drivers is based on replacing the diode in conventional converter topologies (i.e. buck, boost or buck-boost) by a string of High-Brightness Light-Emitting Diodes (HB-LED). Hence, the HB-LED string will be working as the rectifier diode and the load, switching at the same frequency of the main switch. In this case, the output current, which is experimentally validated, shows a negative current peak due to the reverse-recovery effect of the HB-LEDs. In order to reduce the reverse-recovery effect on the HB-LEDs, the main switch of the proposed topologies is replaced with a full-wave resonant switch, which makes possible to reduce the di/dt during the turn-off of the HB-LED string, therefore the reverse recovery effect is eliminated. Moreover, the dimming of the HB-LEDs is done by means of changing the switching frequency of the converter, by varying the turn-off while keeping a constant turn-on time. In order to validate the analysis, the proposed topologies have been experimentally tested on a constructed prototype with an output power of 7.5

Efficient Visible Light Communication Transmitters Based on Switching-Mode dc-dc Converters

Visible light communication (VLC) based on solid-state lighting (SSL) is a promising option either to supplement or to substitute existing radio frequency (RF) wireless communication in indoor environments. VLC systems take advantage of the fast modulation of the visible light that light emitting diodes (LEDs) enable. The switching-mode dc-to-dc converter (SMCdc-dc) must be the cornerstone of the LED driver of VLC transmitters in order to incorporate the communication functionality into LED lighting, keeping high power efficiency. However, the new requirements related to the communication, especially the high bandwidth that the LED driver must achieve, converts the design of the SMCdc-dc into a very challenging task. In this work, three different methods for achieving such a high bandwidth with an SMCdc-dc are presented: increasing the order of the SMCdc-dc output filter, increasing the number of voltage inputs, and increasing the number of phases. These three strategies are combinable and the optimum design depends on the particular VLC application, which determines the requirements of the VLC transmitter. As an example, an experimental VLC transmitter based on a two-phase buck converter with a fourth-order output filter will demonstrate that a bandwidth of several hundred kilohertz (kHz) can be achieved with output power levels close to 10Wand power efficiencies between 85% and 90%. In conclusion, the design strategy presented allows us to incorporate VLC into SSL, achieving high bit rates without damaging the power efficiency of LED lightin

Adaptive Automotive Lighting Systems

Over the past few years, the use of LEDs within the automotive and avionic industries has increased due to their high efficiency, durability and wide range of light brightness. As the use of LEDs within these industries grows, a need for reliable, high performance drivers becomes more relevant. Companies are implementing LEDs for applications involving adaptive lighting or simple dimming features. This thesis shows implementation of various non-isolated analog converters integrated with digital dimmers to achieve these adaptive lighting systems. Adaptive lighting systems involve reading an input from an external source (brake pedal or steering wheel) and changing the brightness and/or pattern of the brake/headlights to convey more information to the driver and their surroundings. The analog converters will implement Linear Technology’s LED driver IC’s, while the digital dimmers comprise of microcontrollers and discrete components. The design, simulation, and hardware verification will showcase the abilities of these analog converters. Results will demonstrate the proposed applications for both adaptive front and brake lighting