Circuito para acionamento e controle do fluxo luminoso de LEDs aplicados em sistemas de iluminação circadiana

Abstract

This work presents some concepts associated with power electronics, filters, electronics, programming and control for the development of an integrated Buck-Boost Forward converter to drive LEDs (Light-Emitting Diodes) applied in circadian lighting systems. Based on the motivation presented, it was sought to develop a system for do tests on low power LEDs, covering the stage of power supply and control of the luminous flux, being necessary to activate them with considerable voltage at the output, due to the series connection of the LEDs in the lamp. In addition, with the variation of the luminous flux of the LED, it is necessary to control the converter to maintain the power at the output, requiring the design, instrumentation and control of this system. Within the scope of this work, the theoretical study, system components design that make up the power and control stage, simulation, prototypes and practical tests are part of the scope of this work. Simulations were carried out for theoretical validation, using MATLAB® and PSIM® software, in addition to the design and practical test of the converter, instrumentation and control system. The results obtained in practice operating in open loop demonstrated the correct design of the converter, where the waveforms were similar to the theory, but the current values were below the reference value, due to the switching losses and the converter elements losses, which were not accounted for due to not being the main focus of the work. The closed-loop tests demonstrated in practice the importance of the converter's relationship with the load behavior. The tests with LED load did not obtain the expected result, due to the sudden reduction of the current when the duty cycle reduction occurs. This is due to the reduction of the output voltage to a value below the threshold voltage of the LEDs, impacting the increase in the bus voltage and current that circulates in the main inductive elements of each stage of the converter. For a resistive load, the tests occurred as expected, managing to switch the load with a value below the reference, due to waveform distortions and sensor measurement error. The fact that the system works in closed-loop with resistive load is due to the fact that the resistive load does not exist, the condition that the LEDs have in relation to the minimum voltage to conduct current and its relation with the Forward characteristic cannot operate without load. Comparing the simulation and practical results, the importance of considering some characteristic factors of LEDs in the theoretical project is highlighted, avoiding discrepancies between the results. In addition, the points where the project needs to be improved are reinforced by proposing items on which it is necessary to have a special focus for this system to work for this application.