Research On The Topology And Control Strategy Of Hybrid Converters Without Electrolytic Capacitor

LED,as an emerging lighting device,has become popular among the public due to its small size,high luminous efficiency,long lifespan and wide range of applications.As a current-driven device,LED requires stable low voltage DC power supply for driving.Existing LED drivers use EMI circuits and electrolytic capacitors to ensure stable operation.However,electrolytic capacitors have a large volume which makes it difficult for the circuit to achieve high power density,and reduces the lifespan of the converter.Although two-stage and multi-stage LED drivers have a simple design and high power factor,their multi-stage energy transfer results in low efficiency,which is not in line with the trend of lightweight and miniaturization of LED drivers.Hybrid LED driver’s topology includes isolated LED driver and non-isolated LED driver without transformers.Based on the analysis of the current situation of LED power supplies,this paper focuses on optimizing the topology and control strategy of the hybrid single-stage capacitor-less LED driver,aiming to improve its lifespan,enhance stability and safety,increase efficiency and power factor.The research is carried out in detail as follows:(1)An isolated virtual three-terminal PFC converter with power decoupling capability is proposed.This converter adds a third terminal consisting of a diode and decoupling capacitor to the traditional flyback circuit.Only a small amount of ripple power is converted through the third terminal,allowing for the use of ceramic capacitors instead of electrolytic capacitors with a capacity of 30×1μF,and improving conversion efficiency.Near zero-voltage-switching is achieved without additional components through resonant coupling between parasitic capacitance,leakage inductance,and excitation inductance.The high voltage stress on the decoupling capacitor is eliminated by changing the driving strategy.At an average output of 0.8A,the maximum ripple rate is only 3.89%,indicating good ripple suppression.(2)A non-isolated high power factor converter with power decoupling and power factor correction capability using non-electrolytic capacitors has been proposed.A common mode analysis model of the proposed topology is constructed to suppress common mode current by optimizing the shared grid and load ground,avoiding reliance on the transformer.Redundant components are eliminated by time-sharing switch and inductor to achieve power set-point decoupling.The filtering inductor also participates in energy buffering,allowing for the use of 6×1μF ceramic capacitors for set-point decoupling.At an output current of 900 m A,the maximum ripple rate is only 8.2%.Moreover,with a power factor greater than 0.984 and THD less than 4.9%,the proposed converter demonstrates good performance.This thesis analyzes the working principles of two kinds of hybrid AC/DC converters,introduces device selection and control circuit design,and demonstrates the effectiveness of the proposed converters through experimental prototypes.The mismatch between the lifetimes of the electrolytic capacitors and the overall system lifetime is addressed,improving the overall system lifetime of hybrid LED converters.