출력전압 밸런싱이 가능한 고승압비의 공진형 컨버터

Abstract

In this thesis, we propose a high step-up resonant dc-dc converter that can achieve voltage balance of the resonant capacitors in distributed generation systems. By incorporating a switching mechanism on the secondary side, we achieve high step-up voltage gain with a minimum number of devices and without reverse-recovery problem. An active-clamp circuit installed on the primary side suppresses the surge voltage that occurs at switch components, recycles the energy stored in the leakage inductance, and provides an alternate resonant-current path formed by the leakage inductance and the output resonant capacitors. A dual resonance that occurs at the secondary side of the converter is exploited to reduce the turn-off current and switching loss significantly, and to achieve high power conversion efficiency. The resonant capacitor voltages remain in balance because the duty cycle of the primary-side switches is always set to 0.5 regardless of the input voltages and load variations. After that, a bidirectional operation is achieved using the proposed converter. In backward operation, it operates as resonant buck mode and transfers the energy from the high-voltage side to the low-voltage side. However, instantaneous reactive power occurs under the heavy load condition. With certain shifted PWM signals, the instantaneous reactive power is reduced. Also, if we overcompensate the phase, the instantaneous reactive power also occurs. This will cause higher current peak and conduction losses. Thus, we have to accurately compensate the phase-shift value. Design and analysis of the proposed converter are presented, and tests using a 400 W experimental prototype verify its superior performance.