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This study presents a novel single-switch high step-up dc-dc converter employing a quasi-resonant operation with high efficiency and low ripple continuous input current characteristics. In order to achieve a high voltage gain, a combination of coupled inductor and switched capacitor techniques is used in the proposed dc-dc converter. Moreover, utilising a series resonance capacitor with the leakage inductance of the coupled inductor leads to a resonant circuit. Subsequently, by employing a quasi-resonant operation, the switching loss of the proposed dc-dc converter has been reduced significantly. Operational analysis, mathematical derivation, component voltage and current ratings are well demonstrated in this study. Finally, the performance of the proposed circuit is evaluated through a 200 W laboratory prototype with 25 V input voltage and 400 V output voltage. The maximum efficiency achieved at full load is 96.4%.

Summary This paper presents a novel transformerless semi‐quadratic buck‐boost converter (SQBuBoC). In the proposed SQBuBoC, two power switches with simultaneous operation are used and a higher step‐up/step‐down voltage conversion ratio is achieved compared with the traditional buck‐boost, Cuk, single‐ended primary‐inductor converter, and Zeta converters. The positive polarity of the output voltage, along with low ripple continuous input current and common ground between the source and the output voltages, are some features that make the suggested topology more suitable for many applications with wide range of output voltage such as photovoltaic systems. Moreover, the total voltage stress across the power switches in this converter is lower than the cascade boost, and the traditional buck‐boost converters led to power MOSFETs selection with lower drain‐source ON resistance (Rds) and efficiency improvement. All the steady‐state analysis and comparisons in continuous conduction mode (CCM) are discussed in details. In addition, to study the low frequency behavior of the SQBuBoC by means of the state‐space averaging technique, the small and large signal models of this converter in CCM are presented. Finally, the SQBuBoC analysis is justified using experimental results of a 50 W step‐up 25 V to 120 V and a 28 W step‐down 25 V to 14 V laboratory prototypes.

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