Winding the Field, Not the Wire: Overlaying Magnetics to Improve Current Dynamics in Modular Power Electronics

Modular power electronics scale power capacity by distributing it across cascaded modules. State-of-the-art modular multilevel converters further introduce dynamic inter-module switched-capacitor exchange and balancing through parallelization. In larger converters, however, this mode needs inter-module inductance to control the equilibration currents. Specifically, differential-mode inductance limits these currents, but existing solutions require conductor re-routing and introduce parasitic resistance. This work presents a non-intrusive resistance-free differential-mode inductance solution: a figure-of-eight-shaped magnetic core that guides the magnetic flux path around existing conductors, such as high-current bus bars. This design adds differential-mode inductance without modifying the conductors. We fabricated a core that provides a 1.52 uH differential-mode inductance while suppressing the common-mode inductance to only 7% of the DM inductance. The core reduces the inter-module current surge from 20.46 A to 7.76 A. The original conductors remain intact.