Research On Interleaved LLC Resonant Converter

Benefited from the soft switching characteristic, LLC resonant converter has good performance at high switching frequency. Therefore it is widely used under the trend of Miniaturization and high frequency of power supply. When the converter works at lower frequency, rectifiers of transformer secondary side turn off with zero current, which cause the large ripple of output. Thus much filter capacitor high cost is necessary. To improve this problem, two-phase interleaved LLC resonant converter is researched in this thesis. After interleaved, the output current of two phase is added, which ensures Continuous current and low ripple. Meanwhile, the Power density of converter is increased.In this thesis, a load sharing scheme of interleaved LLC resonant converter is designed. Due to the circuit component tolerances, the output current of two phase of interleaved LLC are not equal. On the basis of LLC steady state equivalent model, how resonant components’ parameters affect the performance of load sharing is analyzed by adjusting the parameters of the resonant components. Switch controlled capacitor is added into resonant circuit, the capacitor is in series with previous resonant capacitor, which is called equivalent resonant capacitor.The control strategy of closed-loop system is designed. The control strategy includes design of voltage loop and current loop. On the basis of small signal model of LLC resonant converter, the transfer function of switching frequency to the output voltage is obtained, and then compensator of voltage loop is designed. The frequency characteristic of control angle to output current using soft simulation, then compensator of current loop is designed which implemented load sharing. Simulation of closed-loop system is performed to verify the theoretical design.Experimental system has been set up. Control circuit, including drive circuit 、sampling circuit, and DSP control software are designed. After experimenting, the output wave is analyzed. The system, with a good dynamic response performance and low voltage ripple, has realized inter leaving of LLC and zero voltage switching.