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In this article, a novel dual active clamp converter with high voltage gain is proposed for dc–dc applications. The active clamps’ switches turn on and off under zero-current switching (ZCS). In addition, the main switch turns on under ZCS condition, as well. Therefore, switching losses are significantly reduced. The converter is also capable of operating under quasi-resonance (QR) mode. In this mode, switching losses are reduced further by lowering the voltage and current, at which the main switch turns off . In comparison with the conventional interleaved converter, the voltage gain of the proposed converter is almost the same, but the number of semiconductors and switching loss are significantly reduced. The switching frequency of the active clamps’ switches is half of the main switching frequency. The operation principles of the proposed converter are studied in both pulsewidth modulation and QR modes, and the advantages are investigated. A 200-W prototype is implemented to validate the desired functionality of the converter, and experimental results are compared in both modes.

A novel semi-isolated high step-up double-input converter with current-fed inputs is introduced in this study. The proposed converter can operate in double-input mode and single-input mode. It can manage the collected power from both inputs effectively. In addition, it makes a gentle transition between the modes, without the need for an abrupt change in pulse pattern, and does not utilise a breaker switch. Meanwhile, the converter preserves soft-switching as well as a few number of semiconductors (three switches and three diodes). These items have improved the efficiency of the converter to 94.5%. Moreover, it is a high-voltage gain (more than 13). Also, both input ports are current-fed, so the input currents are smoothed. These features make the converter compatible with hybrid renewable energy applications. Furthermore, all components are engaged in both modes, which results in an improved component's utilisation factor. A thorough analysis has been conducted to prove the characteristics mentioned above of the proposed converter. Theoretical analysis has been verified by simulation and experimental results of a 200 W prototype.

A new partly isolated three-port converter is introduced in this study for hybrid energy applications. Two boost circuits form the main input port and a bidirectional battery port of the converter. Therefore, both of them are of a current-fed type, making the converter more suitable for renewable energy applications. In addition, the boost circuits are benefited from a mutual active clamp circuit. The circuit in cooperation with the leakage inductance of transformers provides soft switching, while employing a few number of semiconductors. Furthermore, on the secondary side, two voltage-doubler rectifiers are merged. As a result, the converter employs less number of components, which participate in all power conversion modes. Since most of the renewable energy sources have a relatively low voltage level, the converter retains high voltage gain. These features have resulted in an efficient and inexpensive converter. A thorough analysis has been made and justified by simulation and experimental results.

A high voltage gain dual interleaved full bridge converter with Zero Voltage Switching (ZVS), improved integrated magnetics, and a new resonant Switched -Capacitor-Cell (RSC) is presented. By taking the advantage of a new resonant switched capacitor cell and transformers with low turn-ratio as well as low leakage inductances, the desired high output voltage can be obtained. Furthermore, the output diodes operate in Zero Current Switching (ZCS) condition, and switches are maintained under ZVS condition over the whole range of output load variations. In addition, switches turn off near zero current leading to high overall efficiency. An interleaved approach (multi-cell) is adopted over a single cell to increase the power handling capacity. Furthermore, transformers of dual cells are integrated into a single UU core which cuts down the total volume of the converter as well as the total core loss. Since secondary windings have opposite polarities, there exists no DC flux, and the top and bottom RSC cells operate in 180 degree out of phase. Taking the aforementioned characteristics into consideration, the proposed converter has a good performance for high voltage applications. Experimental results of a 3 kw prototype with an output voltage of 16 kV validate the features of this topology.

A quasi-resonant dc–dc converter with high voltage gain and low current stresses on switches is proposed in this paper. This converter preserved inherent advantages of current-fed structures, for instance, zero magnetizing dc offset, low input ripple, and low transformer turn ratio. Moreover, by employing the active-clamp circuit, the voltage spikes across the main switch, due to the existence of leakage inductance of the isolating transformer, is absorbed, and switches work in zero voltage switching. Since quasi-resonant switching strategy is employed, turn-off current (TOC) and losses of switches are considerably reduced. Because of zero current switching (ZCS), reverse recovery problem of diodes is alleviated. Experimental results on a 150-W prototype are provided to validate the proposed concept.

This study describes a duty-cycle-controlled resonant dual-half-bridge converter with multifunctional capacitors for enhancing the voltage level of fuel cell and photovoltaic sources to 380 V. Owing to the incorporation of dc-link capacitors and leakage inductance into two various resonant circuits, both switches turn-on under the zero-voltage-switching circumstance and turn-off with low current because of quasi-resonant operation. Since the currents of diodes are controlled by the leakage inductances of transformers, it is not obligatory for a designer to employ the diodes with reverse-recovery current specification; consequently, less expensive diodes can be adopted. The complementary effects of series-connected secondary windings of transformers and switched-capacitor circuits result in forming the balanced voltage multiplier stage, augmenting the voltage conversion ratio substantially without the need for utilising a transformer having higher turns ratio; so, one of the magnificent factors of growth of the conduction losses has been avoided. Ultimately, the results of the laboratory prototype operating with 58 kHz switching frequency, 18 V input voltage, 380 V output voltage, and 500 W output power prove that the proposed topology would be proficient to fulfil its function in systems using distributed generation resources.

Summary This paper presents a high step-up soft switched dc–dc converter having the feature of current ripple cancelation in the input stage that is specialized for power conditioning of fuel cell systems. The converter comprises a special half-bridge converter and a rectifier stage based upon the voltage-doubler circuit, in which the coupled-inductor technology is amalgamated with switched-capacitor circuit. The input current with no ripple is the principal characteristics of this topology that is achieved by utilizing a small coupled inductor. In addition, the low clamped voltage stress across both power switches and output diodes is another advantage of the proposed converter, which allows employing the metal–oxide–semiconductor field-effect transistors with minuscule on-state resistance and diodes with lower forward voltage-drop, and thereby, the semiconductors' conduction losses diminish considerably. The inherent nature of this topology handles the switching scheme based on the asymmetrical pulse width modulation in order for switches to establish the zero voltage switching, leading to lower switching losses. Besides, because of the absence of the reverse-recovery phenomenon, all diodes turn off with zero current switching. At last, a 250-W laboratory prototype with the input voltage 24 V and output voltage 380 V is implemented to verify the especial features of the proposed converter. Copyright © 2015 John Wiley & Sons, Ltd.

A soft-switched dual-boost coupled-inductor-based converter is proposed which possesses an intrinsic advantage, in terms of transferring the energy directly to output to provide the essential voltage and power for load. The fabulous characteristic of the proposed structure, the combination of forward and flyback converter, makes it possible to utilise one magnetic core for two coupled inductors, advancing the power density. Another implication of proposed converter is the fact that leakage inductances pave the way for the zero-current-switching implementation by confining the diodes current slope during turn-off period. As regards the voltage conversion ratio, the secondary windings of the coupled inductors operate in series with the capacitors of both voltage-doubler stage and capacitor-diode stages; consequently, designer is under no obligation to use coupled inductors with extreme turn ratio. Concerning the mentioned features of converter besides its high-efficiency power conversion over a broad range of input voltage, the proposed structure is well suited for the purpose of high step-up dc–dc converter. Lastly, the results of laboratory prototype, working with switching frequency of 50 kHz and output voltage 380 V, are convincingly in line with the mathematical analysis.