Digital LLC Resonant Converter And Parallal Current Sharing Research

With continuous development of information technology, the reqirements of power supply in telecommunication servers and computers are growing rapidly. High efficiency and high power density is always the main driving force for the development of modern power electronics technology. Resonant converter has less switching loss, higher switching frequency, lower EMI and smaller volume compared with conventional PWM converter. LLC resonant converter is a new soft switching converter which can operate in the wide input and full load range with Zero Voltage Switching(ZVS) in primary switches and Zero Current Switching(ZCS) in secondary rectification diodes at the same time. So that switching frequency can highly increase and volume can be reduced without increasing the switching losses. In addition, most parasitic parameters of the converter can be used for implementing ZVS and will beneficial for components integration and increasing the power density. For these reasons, LLC resonant converter is considered as the topology which matches the power supply development direction, and it has great research value.The paper introduces the development of high frequency switching power supply and indicates the importance of soft switching technology for high frequency power supply. After studying the operation principle of LLC, the First Harmonic Approximate model has been established to analyze the transmission gain and impedance characteristic of LLC, and derive the ZVS condition. The paper also analyzes LLC operation process in different status, and proposes an optimized design method and gives the detailed design proceduce.Digital control is a new trend of power supply development because of its flexible configuration, short development cycle, high integrated level and convenient upgrade. The paper designs a LLC resonant converter with TI’s new generation digital power controller UCD3138, developed software to implement functions such as synchronous rectification, constant current and power control, current sharing and various protections. The computer can communicate with the converter through PMBus for real-time supervising and management. Theoretiacl analysis and the proposed design strategy has been verified by experiment results.