Coupling Dynamics of Second-Order Harmonic Active Filters in Single-Phase Input-Series/Output-Parallel AC-DC Converters

Abstract:
Input-Series/Output-Parallel topologies are viable and promising solutions for MV/LV conversion. In case of single-phase ISOP AC/DC converters, all the input stages suffer a second-order harmonic ripple affecting their floating DC-bus voltages, which can propagate to the output stage. A solution to mitigate or eliminate it is to use active filters. However, uncoordinated operation of active filters may show unexpected coupling effects among the different modules of the ISOP converter. This paper analyzes and compares the effects of unbalanced active filters functioning for different operating modes, and proposes a simplified equivalent circuit to analyze this phenomenon.