Three-level forward-flyback phase-shift ZVS converter with integrated series-connected coupled inductors

In this paper, a novel three-level Forward-Flyback phase-shift converter is proposed for high-input voltage and high-efficiency applications. The primary-side structure of this converter is similar to that of the conventional three-level phase-shift converters, which makes the switch voltage stress only half of the input voltage and the voltage on the capacitor divider autobalanced. There are only two coupled inductors in this converter and each coupled inductors has two windings. The primary windings of the two coupled inductors are in series to achieve buck-type conversion. And their secondary windings operate in the interleaved mode to sustain the large current. The coupled inductors operate in Flyback and Forward modes to enhance the magnetic core utility rate. Furthermore, the two coupled inductors can be integrated into a magnetic core to further improve the power density. In addition, zero-voltage-switching performance of the inner switches at light load condition can be provided because the magnetizing current can be employed to charge and discharge the parallel capacitors. As a result, the switching losses are minimized at a wide load range. A 500V prototype is tested to verify the advantages of the proposed converter.