Design On Two-stage Bi-directional Converter

With the shortage of global energy and the increasingly serious environmental pollution problems, people attach more importance to the new technology of energy saving and emission reduction.Aiming at the two-stage bidirectional converter, two modules are designer respectively. Meanwhile, the power density and efficiency are improved.In this paper, the status of two-stage converter is analyzed, including former AC/DC converter and the latter bi-directional DC/DC converter. By comparing the advantages of all kinds of specific topology, the single phase full bridge AC/DC rectifier and the half-bridge LLC resonant topology are selected. The converter is mainly used in a small voltage and high current situation. To reduce the current ripple, the LLC resonant converter uses a two parallel symmetrical topology. The principle of the forward LLC resonant converter is analyzed; the ideal area is determined by the fundamental model, which provided a theoretical basis for the designing of the main circuit parameters. At the same time, a precise loss model is established. A reasonable driving digital program for the transformer secondary synchronous rectification is provided; the efficiency of the LLC resonant converter is further enhanced. Simulation of closed-loop system is performed to verify the theoretical design.A distributed control strategy is used for the converter, which ensures the system operating at unity power factor status. According to the requirements of design index, it carried out the parameter design the main circuit components; The extension method of describing function(EDF) is used to build a small signal model, the transfer function of switch frequency to the output voltage is obtained, and then compensator of voltage loop is designed.A 1.8 k W prototype is made and measured in order to test the performance.The experimental results show that the prototype can realize the functions, including forward rectified charging mode, the switch control between charging mode and discharging mode.The system also has a good dynamic response performance and steady-state response performance.