In this article, an ultrahigh step-up quadratic boost converter based on coupled-inductor is proposed. The voltage gain of the proposed converter can be enhanced significantly by increasing the duty cycle due to the quadratic boost structure. A coupled-inductor integrated with a voltage doubler cell is applied to further improve conversion ratio and reduce voltage stresses. The leakage inductor current is utilized to achieve zero-current switching for output diode . Meanwhile, high efficiency is possible as the energy of the leakage inductor is recycled and transferred to the load. The operating principle and steady-state analysis are provided, and a 280-W prototype is designed to verify the validity of the proposed converter.