| LLC resonant converter is widely used because of its high power density and high efficiency.It can realize zero-voltage switching for primary side switches in a wide input voltage or full load range and zero-current switching for secondary side rectifiers in specific working area.Firstly,different modes with specific characteristics at different working areas of LLC resonant converter are analyzed in detail.By the First Harmonic Approximation method,the equivalent circuit is obtained and then the voltage gain equation and curves can be written and drawn,the ideal operating area of the resonant converter is chosen.The influence of different parameters towards voltage gain curves and operating states is analyzed.Then,Chapter Three analyzes the operating principles and regulation processes of various charge control strategies under the condition of input voltage or load disturbance.The simulation model of LLC resonant converter is built by using UCC256302 to implement the hybrid hysteresis control strategy.The small signal model is established and the dynamic process of the converter output voltage is simulated and verified when the input voltage or load disturbance occur.Finally,based on the application of 500 W 270V/28 V,parameters of a prototype are designed in detail to validate theoretical analysis.In order to improve the power density,various integrated magnetic designs are studied and the expressions of resonance parameters are given.Meanwhile,the loss of main components in the converter is analyzed.The experimental waveforms and efficiency curves of prototype are given. |
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