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Comparative Overview of Power Balance Control for Two-stage and Single-stage Isolated MVAC-LVDC Cascaded Converters

Abstract:

Power routing imbalance through the sub modules of a cascaded isolated medium-voltage AC - low-voltage DC (MVAC-LVDC) converter is inevitable due to the unavoidable drift/mismatch in values of passive components. In this paper, a comparative overview of the power imbalance issue and its mitigating control technique along with pertinent analysis is discussed for two-stage and single-stage isolated MVAC-LVDC cascaded converters. It is observed that for a two-stage conversion architecture, apart from the 2Nf-{sw} grid-current harmonics, characteristic of a cascaded multilevel converter, some lower order switching frequency based harmonics remain. On the other hand, for the single-stage conversion architecture counterpart, the dominant switching frequency based grid-current harmonics appear at 2 f-{sw} • The respective power balance control (PBC) schemes for the two conversion architectures are found to be effective, and the PBC reinforced single-stage converter displays lower grid-side current's THD compared to its two-stage counterpart. A suitable experimental verification of the implemented PBC strategy on two-stage and single-stage cascaded converter topologies is presented to demonstrate their comparative performance.