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Three-phase Interleaved LLC Resonant Converter with Integrated Planar Magnetics for Telecom and Server Applications

Fig.1. Schematics
The LLC converter is the most suitable topology for DC/DC converters in server and telecom applications. In order to increase the output power and reduce the input and output current ripples, the three-phase interleaved LLC converter is becoming more and more popular. By conecting the three phases of the converter in a certain way, the three-phase LLC converter has the benefit of automatic current sharing. Different topologies of three-phase LLC converters are surveyed in this paper. A new topology suitable for high-frequency operation is proposed, 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, full-bridge secondary side due to high-frequency operation, and shielding technique to reduce common mode (CM) noise. The three-phase LLC converter suffers the drawback of numerous and bulky magnetics. A novel magnetic structure is proposed to integrate three inductors and three transformers into one magnetic core. 600 V GaN devices from Panasonic Corporation and 80 V GaN devices from Efficient Power Conversion Corporation (EPC) will be employed for the primary and secondary, respectively. By pushing the switching frequency up to 1 MHz, all the windings for the magnetic structure can be implemented with 4-layer PCB winding. Additional 2-layer shielding is integrated in the PCB windings to reduce CM noise. A 1 MHz 3 kW 400 V to 48 V three-phase LLC converter with the proposed magnetic structure is designed with an estimated peak efficiency > 98 percent, as shown in Fig. 2, and a power density of > 200W/in3.
Estimated efficiency
Fig. 2. Estimated Efficiency