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IEEE Journal of Emerging and Selected Topics in Power ElectronicsAbstract-A new class of high-voltage-gain DC-DC converters for high efficiency and transformer-less DC-DC applications where large voltage step-up ratios are required, is presented in this paper. The converter is derived from the hybrid integration of a switched-capacitor converter and a boost converter. It features high step-up voltage conversion ratio with a moderate duty cycle; non-pulsating input current; low voltage stress on all of the switches; easy implementation of control and driving circuits; scalability for high current high-power applications; and low cost due to reduced components via combination of a two-stage converter into a single-stage converter. Full soft-charging operation and minimal device voltage stresses are achieved under all operating conditions. Steady-state operations of the converter are comprehensively analyzed. A 300 W prototype of a 19-time converter achieving the peak efficiency of 96.1% is built. Both simulation and experimental results validating the theoretical analysis and operation of the converter are provided.

High-step-up DC/DC converters are widely required in grid-connected applications with renewable energy sources. An extremely high-ratio step-up non-isolated DC/DC converter, in the form of a harmonics-boosted resonant converter, is proposed in this paper. This proposed converter consists of a high-frequency DC/AC inverter stage that is followed by a passive AC/DC rectifier stage connected in cascade. Conventionally, such a DC/AC inverter is designed to output a pure sinusoidal AC voltage with an amplitude several times the amplitude of the input voltage. However, for the proposed converter, the harmonics-boosted inverter stage is designed to contain selected voltage harmonics that significantly boost the amplitude of its output voltage. This greatly increases the overall gain of the converter. The adopted AC/DC stage is a diode-capacitor rectifier, which is of high efficiency and easily extendable to increase the voltage gain. Importantly, the proposed converter involves only one active switch.With only one active switch, the driver's loss is minimized and the converter's control is simplified. Zero-voltage switching (ZVS) is applied to reduce the switching loss, which also allows the converter to operate efficiently at high frequency, and thus can be designed for high power density. The optimal design of the two converter stages and their combined voltage gain is investigated and reported. Besides, a design guideline of the proposed converter is provided. A prototype of a 57-time harmonics-boosted resonant converter with 3.3 V input voltage, 500 kHz switching frequency, and 21 W output power, is built. The experimental result shows that the achieved converter's efficiency is as high as 88.6%.