Sliding Mode Control of a Ćuk converter with variable hysteresis width for HBLEDs applications

Despite their high cost, High-Brightness LEDs (HBLEDs) have high competitiveness in the market, due to the high efficiency that can be achieved. The efficiency requirement should be completed by means of the voltage conversion stage by performing Power Factor Corrector. In this paper we consider the problem of PFC and output current regulation for a group of HBLEDs by using a Ćuk converter under a Sliding Mode Control which must be ultimately implemented by a hysteretic comparator to limit the switching frequency to practical values. However, with a constant hysteresis width, the system exhibits harmful harmonic distortion in the input line current waveform. Therefore, a variable hysteresis window is used thereby avoiding this distortion near the zero crossing of the input current. Using the Ćuk converter under SMC with variable hysteresis window, the converter will be imposed to behave as a Loss Free Resistor (LFR) which acts as an ideal rectifier with very low harmonic distortion and therefore with a power factor near unity.