Research On LLC Resonant DC/DC Converter

To improve the switching frequency is the most efficient way to decrease the converter volume, to increase the converter efficiency and to uprate the power density among DC/DC converters. Compared with the conventional PWM converter, the resonant converter is with advantages such as a wide range of input voltage, high efficiency, small volume and light weight, besides, the power tubes within the transformer primary side of the LLC resonant converter is capable of realizing zero-voltage on within the whole load range, the rectifier diodes on the transformer secondary side is easy to realize zero-current off, meanwhile, the resonant inductance and the transformer is easy to realize the component integration, thus a wide range of attentions have been paid in this area.In this dissertation, after the steady-state performance comparison among series resonant converter, parallel resonant converter and series-parallel resonant converter, a novel LLC resonant converter topology has been proposed. the proposed topology has a relative low circulation energy and relatively high efficiency under the high input voltage. The FHA equivalent circuit model of LLC resonant DC/DC converter is set up according to first harmonic approximation method and its transfer function of DC voltage gain after normalization is deduced. And the no-load characteristic, short circuit characteristic and impedance characteristic under different frequency ranges are analyzed, which lay a theoretical basis for the resonant converter parameter designing. The simulation model for LLC DC/DC converter control system is set up within MATLAB/Simulink, and the superiority of LLC resonant DC/DC converter with the adoption of frequency variation control strategy under different input voltages and loads is verified by the simulation results comparison. Besides, the designing of control circuit which is centered with L6599 A and feedback circuit are also illustrated. The designing details of the peripheral resistors and capacitors are well elaborated. Finally, the hardware designing and set up of LLC resonant DC/DC converter is conducted, and the experimental waveforms are analyzed to verify the validation of theoretical analysis.