A Frequency Independent Closed-Loop Frequency Dithering Technique to Attenuate Conducted EMI for Dual-Active Bridge Series Resonant Converter

The frequency dithering techniques (FDT) to attenuate electromagnetic interference (EMI) are widely researched in the literature. However, the existing FDTs cannot be applied to resonant converters, where state and output variables are functions of switching frequency. This paper proposes an FDT combined with frequency-independent closed-loop control for dual active bridge series resonant converters (DABSRC). The proposed combined technique attenuates the EMI noise and simultaneously regulates the output variables, making it independent of switching frequency variation. The FDT considers 5 switching frequencies from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$66-72$</tex-math></inline-formula> kHz in steps of 1.5kHz. The proposed FDT considers the effect of resolution bandwidth (RBW) of 9kHz as per EMI standards, which is largely neglected in the literature. The frequency dependency of the output variables is eliminated by a modified large-signal model-based control (MLSMC) through feed-forward cancellation. The proposed technique achieves a significant EMI attenuation of 8dB along with decoupled output voltage and reactive power control. This achieves a filter size reduction by 34%. Additionally, the settling time achieved for output voltage and reactive power is 5ms for a load transition of as high as 62.5%. The results are experimentally validated on a 1.5kW DABSRC prototype.