Topology derivation and experimental platform design for soft-switching high-gain DC–DC converters

Developing distributed renewable energy sources is essential for constructing modern power systems; however, the low output voltages (24–48 V) of these sources do not allow direct connection to high-voltage grid-tied systems or standard 400 V DC buses. Although various high-gain DC–DC converters have been introduced, most suffer from hard-switching losses or lack common-ground characteristics, severely compromising their conversion efficiency and forcing the use of expensive differential probes during experimental testing. To resolve these efficiency and structural bottlenecks, this research designs a new quasi-resonant, soft-switching, high-gain DC–DC converter based on the Sepic topology. The objective is to simultaneously achieve high voltage gain, elevated efficiency, and common-ground characteristics to simplify waveform observation and reduce hardware costs. Crucially, the proposed topology deduction and soft-switching design methodologies are intended for extension into the practical sessions of the “Power Electronics Technology” course to develop students’ complex engineering problem-solving and innovative capabilities.

A systematic methodology spanning topology derivation, mathematical modeling, and experimental prototyping is developed. Starting from the basic Sepic circuit, a Y-source network is integrated to utilize the coupled inductor turn ratio for high-ratio voltage boosting. A passive clamping circuit is implemented to recycle leakage energy and suppress switch-voltage spikes. Then, a three-winding coupled-inductor voltage multiplier cell is embedded, followed by a unique branch reconfiguration strategy to eliminate internal loop conflicts and achieve a stable, common-ground layout. Under continuous conduction mode, the converter exhibits four distinct operating modes within a single switching cycle. A complete mathematical model based on Kirchhoff’s voltage law and volt-second balance is established to derive the formulas for the voltage gain and component stresses. A quasi-resonant mechanism is established via the interaction between the leakage inductance and intermediate capacitors. In particular, the resonance frequency is configured higher than the switching frequency to achieve zero-voltage switching (ZVS) for the switch and zero-current switching (ZCS) for the diodes. Finally, a 200 W experimental prototype is fabricated to verify the operational performance of the proposed converter.

Steady-state experimental tests were conducted on the 200 W prototype under a 37.5 V DC input voltage, with a duty cycle of 0.4 and turn ratios of n₂ = 0.5 and n₃ = 1.5. Under these conditions, the converter steps up the 37.5 V input to a stable 400 V output, verifying a practical voltage gain of 10.67, which closely matches that of the theoretical model. In addition, the main switch operates with ZVS at turn-on with its voltage stress clamped at 60 V, while the clamp and multiplier diodes achieve ZCS turn-off with minimized reverse recovery. Moreover, the average input current is 5.6 A, yielding a peak overall system efficiency of 95.23%. Furthermore, under full-load operation at 23 ℃, the peak component temperature stabilizes at 40.2 ℃, and the low temperature rise of 17.2 ℃ validates the effectiveness of the quasi-resonant loss reduction.

The proposed converter successfully fulfills all design expectations by effectively resolving the trade-off between ultra-high voltage gain and conversion efficiency. Experimental results confirm its high efficiency (95.23%), excellent thermal stability, and high suitability for low-voltage renewable energy integration. Crucially, the common-ground structure simplifies the measurement layout, eliminating the need for expensive differential probes while significantly reducing experimental research costs. Furthermore, the systematic engineering methodology encompassing rigorous topology deduction and soft-switching optimization provides a structured paradigm for the practical modules of the “Power Electronics Technology” course, effectively guiding students through complex engineering problem-solving and enhancing their innovative practical capabilities.