부산대학교 도서관

This paper presents a high-power-density high-efficiency single-phase universal-input to 28V isolated ac-dc conversion system comprising multiple paralleled two-stage ac-dc converter modules. The two-stage converter modules utilize a totem-pole bridgeless boost PFC converter followed by an isolated LLC resonant converter. A new droop control strategy is presented which employs the input current of the secondary dc-dc conversion stage to enable adequate output current distribution between paralleled modules when powering a common output load. The proposed droop control strategy also incorporates a variable droop resistance based on the instantaneous value of the dc-bus voltage to compensate for the effect of the twice-line frequency dc-bus voltage ripple and ensure a stable output dc voltage. To validate the proposed control strategy, two 1-kW universal input-to-28V ac-dc converter modules are designed, built, and tested. The prototype system achieves a current distribution error of less than 0.3% at the peak output power of 2kW while maintaining a high conversion efficiency of greater than 91% across a 3:1 output power range.