Adaptive control for MMC-SAPF with balanced and unbalanced PCC voltage

Three-phase three-wire shunt active power filter (SAPF) with traditional positive-sequence control can only compensate part of the nonlinear load current harmonics if the PCC voltage changes from balanced to unbalanced condition. Changes of both nonlinear load current harmonic components and equivalent circuit for modular multilevel converter based SAPF (MMC-SAPF) are analyzed in the paper. To solve the problems caused by PCC voltage switches between balanced and unbalanced conditions while MMC-SAPF operating, an adaptive control strategy for MMC-SAPF including the voltage unbalance detection and smoothly switching control on enabling/disabling the negative-sequence strategy is proposed. Simulation and experimental tests validate the effectiveness of the proposed control scheme on a downscaled 64V/2kVA apparatus.