In this article, an optimal structure for a high step-up nonisolated dc-dc converter is proposed. In this topology, the required high voltage gain can be obtained with a low number of elements. Furthermore, by implementing an auxiliary circuit, zero-voltage switching condition for the switches is provided, input current ripple has been reduced to almost zero, and all of the power diodes turn off and on under zero-current conditions. In the proposed structure, to regulate voltage gain, the extendable number of diode-capacitor voltage multiplier (DCVM) stages are combined with a coupled inductor. The voltage stresses across the semiconductors can be regulated by the number of the DCVM stages and the turns ratio of the coupled inductor. Thus, it provides two degrees of freedom for the designer to use low-rated semiconductors, which increases the converter efficiency. In this article, the performance of the proposed converter, in terms of voltage stress, voltage gain, and efficiency, has been analyzed, and a comprehensive comparison between the presented topology and other similar topologies presented. Finally, to verify the performance of the proposed topology, a 500 W (40 V/400 V) laboratory prototype has been developed and tested. The experimental results confirm its superiority and suitability.