Research On LLC Resonant Half-Bridge DC-DC Converter

It is very available to reduce the volume and weight of converter, improve the total efficiency and power density with higher operation frequency. Considering from realization, resonant converter has the advantage of higher operation frequency, lower switching loss, wider range of input voltage, higher efficiency, lighter weight, smaller volume, smaller EMI, lower switching stress to PWM converter. The prominent merits of LLC resonant converter can be specified as follows, realization of full load range of ZVS for primary switches and ZCS for secondary diodes, easy integration of resonant inductor and transformer, wide range operation. It is focused on due to the above advantages.LLC resonant converter is developed on the base of components resonant converter by adding a parallel inductance, so its DC gain characteristic is better to series resonant or parallel converter. But on the other hand, it is more complex to control the operation and the design of parameters of converter. Now one of the major difficulties to restrict the development of LLC converter is that engineers are lack of information concerning the way the converter operates and the way to design it easily.This thesis studied three traditional resonant converters first and compared them with LLC resonant converter, then summed up the advantages of LLC resonant converter. Thesis discussed the principle and the operation modes of LLC resonant converter in each frequency range and corrected and supplymented some operating states droped in many literatures. Then discussed the DC gain characteristic based on the FHA, and put forward an easy method to design parameters of converter. At last, the experimental data of the system is given to testify the validity of the design method.In order to design controller, small-signal model of the converter must be given. In this paper, the small-signal model of LLC resonant half-bridge converter is deduced using Extended Describing Function (EDF) method firstly. Also, the characteristic of the small-signal model is analysed and compensatoris designed to meet the requirements of dynamic process, and it is very helpful for pratice. Simulation results prove the correctness of the theory.