Research On Bi-directional Full Bridge LLC Resonant Converter

With the continuous consumption of fossil energy and increasingly serious environmental pollution problems, renewable energy technology is getting more and more attention. The LLC resonant converter can realize zero-voltage switching on the inverter side and zero-current switching on the rectifier side, so this kind of converter has been widely used in various unidirectional converter occasion. How to apply LLC resonant technology to bidirectional converter to achieve high efficiency has become a new resear ch direction in area of power electronics. A new kind of control method of a bidirectional LLC resonant converter has been specifically studied in this dissertation.Firstly, this dissertation compares a variety of specific topologies and chooses the traditional LLC resonant topology as the research target. The forward operation mode of the converter is based on LLC resonant mode, the DC analysis has been conducted too, and a new kind of loss model which considers the harmonic factors is bulit.The analysis and design of the reverse mode is the focus of this dissertation. A new drive control method is proposed and it can realize boost operational function when the converter works in the revrse direction, the detailed analysis of the DC characteristics under the boost control method is analized by means of time domain and state plane analysis. Subsequently, the resonance parameters and the voltage and current stress are designed and calculated for this converter.On the basis of theoretical analysis, simulation of the LLC resonant converter is conducted. The simulation results show that the control method proposed can achieve the ability to work in a boost mode well when the converter works in the backward direction.An experimental platform has been bulit for testing waveforms of the converter. Experimental results prove that the forward work mode of the converter retains LLC resonant mode, and high efficiency is achieved in this mode. A normalized voltage gain which is greater than 1 can be achieved in the backward work mode and some of the soft switching characteristics can be retained too. The experimental results keep consistency with theoretical analysis and these prove the design rationality of this bidirecional converter.