Symmetrical Balanced Circuit for Common-Mode Noise Mitigation in LCL-T Resonant Converter

This paper presents a common mode (CM) noise mitigation technique of a three-element resonant converter at its DC input terminal. Using a novel balanced LCL-T tank structure, that ensures symmetry for CM noise propagation and decouples the effect of secondary side converter, the DC input CM emissions in the conducted EMI compliance range (150 kHz to 30 MHz) are minimized significantly. Unlike traditional methods, the proposed technique is not limited to upper limit of common mode Y capacitors and relies on simple wheatstone bridge balancing principle. As such, the CM filter size can be significantly smaller. The proposed circuit is demonstrated on a GaN based three level LCL-T converter used in On-Board charger applications switching at a fixed frequency of 500 kHz.