This paper presents a new control method and a detailed project methodology for the optimized connection method of two converters, aiming to reduce the redundant power processing, in order to supply high power LEDs with reduced capacitance and high efficiency, directly from the AC line. This connection method allows dealing with two major issues related to the LED driver: capacitance reduction and efficiency increasing. The first converter provides Power Factor Correction (PFC), while the second converter controls the current through the LED. The basic idea consists in making the second converter to process only the low frequency ripple of the first converter, thus smoothing the LED current. In this way, the low frequency ripple is managed by the second stage so that the capacitance of the first stage can be significantly reduced. The proposed control method can achieve better results for the low frequency compensation. Besides that, a high power factor and a low harmonic content are obtained, fulfilling the IEC 61000-3-2 class C requirements. A laboratory prototype with a rated power of 75 W and an input voltage of 220 Vrms/60 Hz was built in order to show the feasibility of the idea. The measured overall efficiency of the converter was 91% and electrolytic capacitors were avoided.
Este artigo apresenta uma estrutura de conversor estático, utilizando processamento parcial de energia, para minimizar capacitâncias em luminárias à base de LEDs aplicadas na iluminação pública, onde potências maiores que 70 W geralmente são requisitadas. A estrutura da topologia é baseada em dois conversores, conectados de maneira que o segundo conversor processe apenas uma pequena parcela da potência total enviada à carga. Além disso, com o intuito de diminuir a capacitância do primeiro estágio, uma estratégia de controle é utilizada com o objetivo de compensar ativamente essa ondulação. Os conversores utilizados, a modelagem matemática e a estrutura do controle são mostrados em detalhes. Um protótipo foi montado, com 75 W de potência para 220 V rms de tensão de entrada, a fim de demonstrar a funcionalidade da ideia e suas principais características.
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