Research On Digital Controlled Bidirectional Full Bridge LLC Resonant Converter

With the development of power electronics technology,the converter composed of power electronic devices is developing towards high efficiency,high frequency,and high-power density,however the conduction loss and switching loss of power switching devices hinder the development trend.To improve the switching frequency of the converter,it is necessary to reduce the switching loss of the power switching device.Therefore,zero voltage zero current soft switching technology emerges as the times require.LLC resonant converter can achieve the transformer primary side power transistor zero voltage switch and transformer secondary side power transistor zero current switch,greatly reducing the switching loss caused by the high frequency of the switch.Firstly,the working principle of the full-bridge LLC resonant converter and its DC gain and frequency characteristics are introduced,the curve of the resonance parameters on the converter characteristics is plotted,and the resonance parameter design is carried out,and the bidirectional LLC resonant converter control circuits are designed,including the sampling circuit,the isolated drive circuit,and the digital implementation scheme of the controller.In this paper,a digital DSP closed-loop control system based on the resonant inductor average current mode for full-bridge LLC resonant converter is proposed,which consists of two loops,an inner current loop and an outer voltage loop.The smallsignal modeling of the full-bridge LLC resonant converter is carried out by the extended function description method(EDF),and the transfer functions such as switching frequency-inductor average current are obtained based on the small signal model of the LLC resonant converter,and the current loop 2P2 Z compensator and the voltage loop PI compensator are designed.Finally,the control circuit and control algorithm were simulated and analyzed by PSIM software,the prototype was developed,and the experimental results were analyzed,which verified the feasibility and effectiveness of the proposed scheme in this paper.The digital DSP control for the bidirectional LLC resonant converter of the new energy energy storage system is realized.