A source-type harmonic energy unbalance suppression method based on carrier frequency optimization for cascaded multilevel APF

Cascaded H-bridge multilevel converter based active power filter can compensate high-order harmonics (17
^th
-50
^th
) in middle-high voltage system with relatively lower switching frequency, but at the same time, a special DC capacitor energy unbalance problem is caused. When the compensation current frequency is close to the witching frequency of the H-bridge cell, harmonic power coupling will lead to the divergence of DC voltages, which is called source-type harmonic energy unbalance in this paper. A carrier frequency optimization method is proposed to suppress the unbalance. This method decouples the harmonic voltage with the output current and minimizes the DC voltage ripple only by appropriately adjusting the carrier frequency. The method is verified by the presented simulation results.