Análise, modelagem e controle de drivers de LED comutados em baixa frequência e conectados à rede elétrica CA

Abstract

The main objective of this work is to study the theoretical and experimental model-ing and control of low-frequency off-line LED (light-emitting diodes) drivers applied to street lighting luminaire. Firstly, some considerations are made about the street lighting system using LEDs and the general characteristics of the LEDs are briefly introduced. The main types of drivers applied in LED luminaires are then presented, with particular focus on the low frequency converters, the ones in which the main switch is gated at twice the line frequency. Next, a mathematical modeling of an LED driver based on the low-frequency switched pre-regulator with CL output filter is performed, which naturally has a high power factor. Design methodologies are presented for two high-power (200 W) low-frequency drivers, one of them with the CL filter at the dc output and the other one with just a capacitive filter (conventional boost pre-regulator ac-dc converter), both of them delivering an average output current of 700 mA and maximum ripple of 15%. A SEPIC-based high-frequency driver is also modeled and implemented, aiming a practical and fair comparison with the low-frequency ones. The comparative study aims at the prototype volume, overall efficiency and losses distri-bution. The open-loop experimental results show that it is possible to achieve high power factor (0.98), high efficiency, (around 94%) and low harmonic distortion of the input current (8.45%) with low frequency drivers. The use of the CL filter at the dc output allows the use of film capacitors instead of electrolytic capacitors, which further increases the converter lifetime. Finally, the small-signal modeling and the closed-loop control design of the low-frequency LED driver based on the boost pre-regulator with a CL output filter were performed. Experimental closed-loop results show that the pro-posed compensator is able to deal with input and load voltage disturbances by keeping the current in the LEDs at the reference value. In addition, the compensator is able to follow the reference, which makes it possible to control the light intensity (dimming).