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This paper describes nonisolated high step-up DC-DC converters using zero voltage switching (ZVS) boost integration technique (BIT) and their light-load frequency modulation (LLFM) control. The proposed ZVS BIT integrates a bidirectional boost converter with a series output module as a parallel-input and series-output (PISO) configuration. It provides many advantages such as high device utilization, high step-up capability, power and thermal stress distribution, switch voltage stress clamping, and soft switching capability. As an example of ZVS BIT, a flyback converter with a voltage-doubler rectifier (VDR) as a series output module is presented and analyzed in detail. In addition, to overcome the efficiency degradation at a light load due to the load-dependent soft switching capability of the proposed ZVS BIT, a control method using a frequency modulation (FM) proportional to the load current is proposed. By means of ZVS BIT and LLFM control, the overall conversion efficiency is significantly improved. The experimental results are presented to clarify the proposed schemes.