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Three-Phase Interleaved LLC Converter with Integrated Magnetics for 48 V Output

Image of Schematics
Fig. 1. Schematics.
The LLC converter is the most suitable topology for dc-dc conversion in server and telecommunications applications. In order to increase the output power and reduce the input and output current ripples, the three-phase interleaved LLC converter has become increasingly popular. Thoughtful connection of the three converter phases allows the LLC converter to have the benefit of automatic current sharing. This paper surveys different topologies of three-phase LLC converters, and proposes a new topology suitable for high-frequency operation, as shown in Fig. 1. The proposed LLC converter employs a delta-connected resonant capacitor network in the primary side to achieve automatic current sharing, as well as a full-bridge secondary side for high-frequency operation. It utilizes a shielding technique to reduce common mode (CM) noise.

The conventional three-phase LLC converter is disadvantageous in terms of numerous bulky magnetics. A novel magnetic structure is proposed which integrates three inductors and three transformers into one magnetic core. 600 V gallium-nitride (GaN) devices from Panasonic, and 80V GaN devices from EPC, Inc. are employed for the primary and secondary sides, respectively. By pushing the switching frequency up to 1 MHz, all the windings for the magnetic structure can be implemented with a four-layer printed circuit board (PCB) winding. An additional two-layer shielding can be integrated in the PCB windings to reduce CM noise. A 1 MHz, 3 kW, 400 V/48 V, three-phase LLC converter with the proposed magnetic structure is designed, as shown in Fig. 2., and high efficiency and a power density of 600W/inch3 are achieved.

Image of Hardware prototype
Fig. 2. Hardware prototype.
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