Research On LLC Resonant Converter

Resonant converter has the advantage of higher operation frequency, lower switching loss, and wider range of input voltage, higher efficiency, lighter weight, smaller volume, lower EMI noise and lower switching stress compared with the 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 and wide range operation. So, LLC resonant converter obtains widespread attention due to the above advantages.The basic classification of resonant converters and the advantages and disadvantages of various resonant converters are comprised and analyzed in the paper. By contrast with PMW converter, LLC resonant converter's main advantages are summarized. The paper takes the 400W LLC resonance converter as the object design. The per-stage is the APFC circuit, and last-stage is the LLC resonance converter.First, the paper carries on the analysis and calculation of the steady-state circuit of LLC resonance converter based on FHA method, and elaborates LLC resonance converter's working principle and operating characteristics in each switching frequency range in detail. Afterward, LLC resonance converter and traditional resonant converter and half bridge PWM converter are compared on the detailed elaboration.Then, the small signal model of LLC resonance converter is established by piecewise-linear method and expansion description function method separately. As the small signal model of LLC resonance converter established by the piecewise-linear method only works in full load situation, the expansion description function method is used to establish a more valid model. This model can directly guide design of the control loop.Then, the integrated design of the whole system is carried on. The design of APFC's main circuit and control and compensation loop are given in the paper. Meanwhile, main circuit of LLC resonance converter is given. But, we need further study and should propose a practical and feasible method to establish control and compensation loop of LLC resonance converter.Finally, a simulation model is established with Pspice. Simulation results show that LLC resonance converter can realize the stability of the output voltage, when the load and input voltage change in a wide range. What's more, it can realize soft-switching of mosfets and diodes. So, the results also prove the validity of the theoretical analysis. However, limited by the experimental condition, the circuit board is still on commissioning.