A high-efficiency converter with high voltage gain applied to a step-up power conversion is presented. In the proposed strategy, a high magnetising current charges the primary winding of the coupled inductor, and the clamped capacitor is discharged to the auxiliary capacitor when the switch is turned on. In contrast, the magnetising current flows continuously to boost the voltage in the secondary winding of the coupled inductor, and the voltages across the secondary winding of the coupled inductor, the clamped capacitor and the auxiliary capacitor are connected in series to charge the output circuit. Thus, the related voltage gain is higher than in conventional converter circuits. Moreover, this scheme has soft-switching and voltage-clamped properties, i.e. the switch is turned on under zero-current switching and its sustainable voltage is comparatively lower than the output voltage, so that it can select low-voltage low-conduction-loss devices and there are no reverse-recovery currents within the diodes in this circuit. In addition, closed-loop control methodology is utilised in the proposed scheme to overcome the voltage drift problem of the power source under the load variations. As a result, the proposed converter topology can promote the voltage gain for a conventional boost converter with a single inductor, and deal with the problem of the leakage inductor and demagnetisation of the transformer for a coupled-inductor-based converter. Some experimental results via examples of a proton exchange membrane fuel cell power source and a traditional battery are given to demonstrate the effectiveness of the proposed power conversion strategy.