| LLC resonant soft-switching technique can realize power converter's ZVS in wide input and full load range for primary switches, easy to achieve ZCS for secondary rectifier diodes, low switching loss, high efficiency, has been a focus in the field of power electronics. In this paper, LLC resonant converter is analyzed in detail and used in the developing of high frequency switching charging cubicle of electric locomotive.LLC resonant converter has three resonant components, the parameters selection of them is very important to realize the high efficiency of the converter. Through detailed analysis on the working principle, a equivalent steady-state model is established using First Harmonic Approximation and the DC characteristics is given,then based on operating point in minimum input voltage/full load and maximum input voltage/no-load, a method on designing the parameters of LLC converter for ZVS is proposed, finally the mothed is checked by simulation.In order to ensure the designed LLC resonant converter has high static and dynamic performance, the converter's controller should be well-designed according to its Small-signal model. Equivalent circuit model method is simple, universal and suitable for modeling of high-order resonant converter. It is used to build the LLC resonant converter small-signal model in this thesis. Based on the model, control-output characteristics is shown and a PI regulator is designed, simulation proved its reasonable.Digital control is the development trend of Power control technique, it can achieve the control scheme by programme, simplify the circuit design, and easy to update. So DSP is selected as control IC in this paper, and based on it, the control circuit, including drive circuit, sample circuit , protect circuit are designed, then the digital PI algorithm and structure of the system software are given.Finally, a prototype circuit for 110V-24V is designed and the experiment results prove the correctness of the theory analysis and designmethod. |
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