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. Design and analysis of the proposed converter are presented, and tests using a 400 W experimental prototype verify its superior performance.