The conventional isolated double step-down DC-DC converter has attractive characteristics for high input voltage and low output voltage applications including a high step-down voltage ratio, low voltage stress for three primary switches, low primary transformer voltage, wide soft-switching range, and no saturation problem. However, this converter still has issues that limit practical application including losing zero-voltage switching in very light load conditions, high circulating current, hard-switching turn-off of primary switches, high voltage ringing, and hard-switching operation of rectifier diodes. This paper proposes a soft-switching isolated double step-down DC-DC converter. By using an active snubber on the secondary side, the proposed converter solves effectively all issues of the conventional double step-down DC-DC converter. The proposed converter can achieve zero-voltage switching turn-on, and zero-current switching turn-off for both primary and secondary switches in the entire load range, while the circulating current and output voltage ringing are eliminated. Moreover, the duty cycle is extended by the control signal of the snubber switch. In this paper, the theoretical analysis, a simulation, and a laboratory experiment are completed with 800 V input, 48 V-2 kW prototype.

This paper introduces a high-voltage step-up isolated quasi-switched series resonant dc–dc converter with a novel PWM method. The primary side of the proposed converter is composed of a quasi-switched boost network and the secondary side consists of a series resonant tank and voltage doubler rectifier (VDR). The proposed topology can achieve soft-switching on the semiconductor devices and performs high efficiency in entire power range. The operating principle, essential characteristics and design guideline of the converter are detailed. A 300 W laboratory prototype with a DC input voltage between 20 and 40 V, a 400 V output voltage, was built to validate the feasibility of the proposed converter.

Many soft-switching techniques have been introduced for non-isolated DC-DC converters in the literature. However, most of them show the results at the low power level. In this paper, an experimental comparison of soft-switching interleaved boost DC-DC converters with auxiliary switches for high-power applications is presented. Two zero voltage transition (ZVT) boost converter prototypes with and without the third diode in the active snubber circuit are built and evaluated. Analysis, operating principles, and parameter design for the ZVT boost converter without using the third diode in the snubber circuit are provided. The experimental verifications from laboratory tests of equivalent 10-kW/50-kHz interleaved boost converters based on discrete SiC MOSFETs and diodes are given. The results are obtained for the input voltage of 200 V and the output voltage range from 320 V to 530 V. The efficiency and power loss distribution of the converters are compared.

Two high voltage gain quasi-switched boost inverters (HG-qSBIs) are introduced in this paper. The proposed HG-qSBIs has the following characteristics: 1) continuous input current with low ripple; 2) reduced voltage stress on the capacitor, switch, and diodes; 3) shoot-through immunity; 4) achieved high voltage gain with single-stage conversion; and 5) improve the output voltage capability with using high modulation index. A novel pulse-width modulationcontrol technique is proposed for the introduced HG-qSBI. Operating principle, circuit analysis, and passive component design guideline of the HG-qSBI are addressed. Comparison analysis between the introduced HG-qSBI and other Z-source-based high voltage gain inverters is presented. A prototype is made to test the introduced HG-qSBI. Simulation and experimental verifications are shown to prove the accuracy of the theoretical analysis.