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A boost-type converter is derived by inserting a third winding of the winding-cross-coupled inductors (WCCIs) between the secondary winding and the output diode of the interleaved flyback converter in this paper. A family of isolated interleaved boost or buck dc/dc converters with WCCIs is summarized by employing the four main types of interleaved structures, which is suitable for step-up or step-down isolated distribution power systems. Then, an interleaved flyback-boost converter with WCCIs and an active clamp circuit is analyzed as an example to explore the advantages of the derived converters. The active clamp scheme is adopted to recycle the leakage energy and to suppress the turn-off voltage spikes on MOSFETs. And only one set of active clamp circuit is necessary for the interleaved two phases. Zero voltage transition (ZVT) soft switching performances are achieved for all MOSFETs during the whole switching transition. Furthermore, the output diode turn-off current falling rate is controlled by the inherent leakage inductance of the WCCIs, and the output diode reverse-recovery problem is alleviated. A clear picture is made in this paper of the general law and structure of the isolated interleaved dc/dc converters with WCCIs. At last, a 650 W prototype with 48 V-to-180 V is built and tested to verify the theoretical analysis in this paper. Index Terms--Active clamp, interleaved converter, winding-cross-coupled inductor (WCCI).

A basic cell with winding-cross-coupled inductors (WCCIs) and interleaved structure is proposed in this paper. A family of dc-dc converters is deduced from the proposed basic cell, which is suitable for high step-up or step-down conversions. The passive-lossless clamp scheme is derived from the active clamp scheme to recycle the leakage energy and to suppress the voltage spikes caused by the leakage inductance. The advantages of the derived interleaved boost converter with WCCIs and passive-lossless clamp circuits are analyzed as an example. The voltage gain is extended and the switch voltage stress is reduced to minimize the conduction losses. The rectifier reverse-recovery problem is alleviated by the leakage inductance. Furthermore, a series of dc-dc converters with WCCIs and passive-lossless clamp circuits are summarized for high efficiency, high power and high step-up or step-down applications. A clear picture is made in this paper on the general law and structure of the WCCIs for dc-dc conversion in high step-up or step-down applications. At last, the simulated and experimental results of a 1 kW 40 V-to-380 V prototype with WCCIs and passive-lossless clamp circuits verify the significant improvements in performance. Index Terms--Basic cell, passive-lossless clamp, winding-cross-coupled inductor (WCCI).

The fundamental limitations of the current topologies for isolated high step-up dc-dc conversion are summarized. The primary-parallel-secondary-series structure is employed in this paper to handle the large input current, sustain the high output voltage and extend the voltage gain. A novel active clamp boost converter with coupled-inductors is proposed for high step-up applications. The third windings of the coupled-inductors have the function of voltage gain extension and the switch voltage stress reduction. The active clamp circuit serves for the interleaved two phases, which reduces the circuit complexity. Both the main and the auxiliary switches of the proposed converter are zero voltage transition performances during the whole switching transition. Meanwhile, the leakage energy is recycled by the active clamp circuit. The rectifier voltage stress is reduced by the primary-parallel-secondary-series structure. The rectifier reverse-recovery problem is alleviated by the leakage inductance. Experimental results for a 40-V-to-760-V converter verify the significant improvements in efficiency. Index Terms--Active clamp, coupled-inductors, isolated boost converter.

An interleaved winding-coupled boost converter is proposed in order to realize ZCS turn-on condition and to achieve high step-up gain. The voltage gain is extended easily and the voltage stress on the switches is reduced with different turns ratios of the coupled inductors. The output diode reverse-recovery problem is alleviated due to the inherent leakage inductor of the winding-coupled inductors. The simple but effective passive lossless clamp circuits are introduced to limit the voltage stress on the switches when they turn off so that the low-voltage, high-performance devices with low conduction resistor can be used in the proposed converter to reduce the relative losses. The leakage energy is ultimately recovered to the load. The high efficiency of 90.7% at full load and the maximum efficiency of 92.6% are achieved in a 1-kW 40-V-input-to-380-V-output prototype for front-end application. There is more than 10% efficiency improvement with the passive lossless clamp circuits compared to the case with RCD dissipated snubbers. The efficiency of 5% improvement at full load is achieved with the proposed converter with passive lossless circuits compared to the conventional interleaved boost converter. Index Terms--Interleaved boost, passive lossless clamp, winding-coupled inductors.