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A Symmetrical Resonant Converter and PCB Transformer Structure for Common Mode Noise Reduction

Fig. 1. Proposed symmetrical structure.
In this paper, using a CLLC resonant converter as an example, a symmetrical resonant converter structure and a symmetrical PCB winding transformer structure are proposed to cancel the CM current through the interwinding capacitor. No additional components are needed, and the interleave between windings is not sacrificed.
A 6.6 kW 500 kHz CLLC resonant converter is built to verify the proposed symmetrical structure. The prototype has 130 W/in3 power density, including the heatsink and cold plate. The CM noise spectrum is tested to demonstrate the superior performance of the proposed symmetrical structure, as shown in Fig. 2. From the measurement results, we can see that the proposed symmetrical resonant converter structure and the symmetrical transformer structure can significantly reduce the CM noise in the system, both for fundamental switching frequency and its high order harmonics.

Fig. 2. Testing results of EMI performance with the proposed split capacitor and symmetrical transformer connection.
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