Differential-Mode Filters with Common-Mode Neutral-Point-Balancing Accelerators for Single-Phase Symmetrical Five-Level Converters

Single-phase symmetrical five-level converter offers a low-harmonic power interface, whose attractiveness is nevertheless affected by dc-link voltage imbalance. Fast rebalancing methods have therefore been proposed, if the natural balancing speed of the converter is intolerable. One possible method is to add a separate parallel RLC branch between the converter and its filter. Being parallel, the branch does not change spectral properties of the converter and filtering properties of the filter, in addition to its robust sensor-less requirement. However, being separated, it does not properly integrate with the filter to explore dual usabilities of the components. This paper therefore proposes a few differential-mode (DM) filters with each having a common-mode (CM) capacitor as the balancing accelerator. The accelerator does not conduct and hence consume no power during the normal balanced condition. It conducts only when an imbalance occurs and directs only those harmonics with fast balancing ability to the dc-link. Its design is simple and can conveniently be performed with an appropriate CM harmonic model. Its performance has ultimately been verified by simulation and experimental results obtained with two different modulation schemes.