ANALYSIS OF ZVS INTERLEAVED LLC RESONANT CONVERTER FOR CURRENT BALANCING IN DC DISTRIBUTION SYSTEM

The power conversion efficiency of an isolated ac–dc converter is a dominant factor in the overall efficiency of dc distribution systems. To improve the power continuity and power conversion efficiency of the dc distribution system, a three-phase interleaved fullbridge LLC resonant converter employing a voltage source converter which is fed by Photo Voltaic System and Wind Energy System is proposed as the isolated ac–dc highfrequency-link power-conversion system. The LLC resonant converter has the advantages of high efficiency, high power density, and low cost. They can be operated at no load condition and at resonance for nominal input voltage. The proposed voltage source converter has the capability of boosting the output voltage without increasing the transformer's turn ratio. Especially, the frequency of the rectifier's output ripple is six times higher than the switching frequency, thereby reducing the output capacitor and the secondary transformer's RMS current. However, the tolerance of the converter's resonant components in each primary stage causes the unbalance problem of output ripple current. It cannot be solved using conventional control techniques since the structure of the three-phase interleaving has the limitations of individual control capability for each converter. To solve the current unbalance problem, a current balancing method is proposed for the output rectifying current.