Study On A Bridgeless Single Stage High Frequency AC/AC Converter

With the persistent advance in packaging technology and the application of new materials, the High-Brightness Light-Emitting Diode(LED) has been increasing its competitiveness over the traditional lights such as fluorescent lamp,incandescent light and so on. Due to its high luminous efficiency, environmentaly-friendly property and long lifetime, LED has been widely employed in large scale LCD panel backlighting, tunnel lighting and street lighting and is promisingly to be the fourth-generation light.In the high power LED lighting applications mentioned above, as the converter between the grid and LED strings——LED driver should realize the following three functions: power factor correction(PFC), galvanic isolation and multi-channel constant current outputs, which traditionally are built in a three-stage stucture. However, the two-stage LED driver has advantages over the traditional three-stage structure in respects of cost and overall efficiency due to its less power conversion stages. A two-stage LED driver consisting of high frequency AC/AC conversion and passive high frequency AC/DC constant current converter is adopted by the paper considering that its modularity structure helps to shorten its development cycle, lower cost and is easy for maintenance, popularization and application. Since the high frequency AC/DC constant current conversion module that can be built by passive resonant circuits has already been studied, the paper is concentrated on the stage of high frequency AC/AC conversion. Therefore, to achieve higher efficiency a novel bridgeless single-stage high frequency AC/AC converter is proposed based on the existing AC/AC converter and drawing research thingking from the existing bridgeless power factor correctors(PFC). Then its operating priciple and working performance is analyzed, and the parameter design of the proposed converter is studied in detail. The main points and achievement of the paper are as follows:Firstly, the topology of the bridgeless single-stage high frequency AC/AC converter, which consists of the toem-pole boost bridgeless PFC and high frequency resonant DC/AC inverter, is deduced and its operating procedure and switching modes are analyzed. Then the converter working performance is analyzed in respects of input power factor, voltage gain, total harmonic distortion of output voltage and soft switching condition.Secondly, according to the working performance of the converter and the analysis of the toem-pole boost bridgeless PFC and the LC-LC series parallel resonant DC/AC invereter, the design procedure for the main circuit component parameters is deduced and the design method is summarized which provides theory consideration for devices selection or design and contributes to the engineering application. Simultaneously, on the basis of designing the input low pass filter for bridgeless single-stage high frequency AC/AC converter taking LC filter as an example, a program design method for low pass filter is summarized which provides reference for designing input filter for singl-stage PFC.Lastly, experimental study on the two-stage LED driver prototype based on the bridgeless single-stage high frequency AC/AC converter is conducted. The complete experimental solution is determined by designing the magnetic elements and the protection circuit for the high frequency AC/DC constant current module as well as design and description for the control circuit and the main chips. Two experimental prototypes of the bridgeless single-stage high frequency AC/AC converter and the one containing rectifier bridge are built and related experiments are conducted.