The Research On Multi-multiplexed Single-stage LED Driving System Based On LLC Circuit

Traditional LED driving systems usually compose of power factor correction circuit and DC/DC converter, though the structure can guarantee high input PF an d low THD, the cost of the structure is high and the reliability is poor. To solve these problems, Recently, single-stage AC/DC converters can reduce the switches number and improve the reliability by switches multiplexing, which receive wide attention recently.However, the existing topologies suffer low efficiency and high bus voltage. To solve the above problems, a novel multi-multiplexed single-stage converter based on LLC circuit is proposed in this paper, which share two switches and improve the reliability of the system. At the same time, the influence factors to system bus voltage has been studied and the optimal design method is proposed. The small signal modeling method for resonant converter has been adopted to compensate the system and design the controller and driving circuit, at the same time, the optimal control method is proposed to reduce the bus voltage at light load condition. The specific contents are as follows:For the losses in single-stage converter based on hard working Flyback circuit is high and the existing single-stage converter based on LLC circuit cannot work in high input voltage condition, a single-stage converter based on interleaved buck-boost converter and LLC circuit is proposed, the single-stage converter achieve power factor correction by the two buck-boost converters wording in DCM, so the PF is very high and THD is very low. At the same time, the two switches are both shared, so the reliability of the system is improved. The working principle of the PFC part and DC/DC part have been introduced detailed and the working modes of the whole system is analyzed.For the common problem of single-stage converter that the bus voltage is very high in light load condition, the energy coupling relationship between buck-boost part and LLC part has been analyzed. Then the different factors that influence the bus voltage are studied. The ratio of leakage inductor and magnetizing inductor greatly influences the bus voltage and value range is studied by bode plot. An optimal design method is proposed based on the analysis and the method can reduce the bus voltage when the input voltage and output power changes.The small signal modeling method for resonant converter which is called Extending Describing Function has been adopted to model th e LLC circuit. According to the modeling results, analog method and digital method are proposed separately to compensate the system and design the controller and driving circuit.To further reduce system bus voltage and improve system efficiency at light load condition, the state plane trajectory method is used to analysis the system working modes, based on the stage plane trajectory method, an optimal digital control method is proposed to reduce system bus voltage and improve system efficiency. A 100 W prototype is proposed and the test results verify the correctness of theoretical analysis. The PF is as high as 0.995, the THD is 5.7% and the efficiency is 91.5% at full load condition.