Optimal Capacitance Design for Three-Phase AC–DC Interlinking Converters Under Unbalanced Conditions

Abstract

Modern distribution networks increasingly integrate single-phase distributed generation and residential loads, such as PV inverters, microinverters, and electric-vehicle chargers, while most commercial infrastructures remain three-phases. This mismatch often leads to phase power imbalance, negatively affecting power quality in the ac grid. In this context, ac-dc interlinking converters play a key role in enabling power exchange between the ac utility grid and dc microgrids. In addition, recent advances in artificial intelligence, model predictive control, and other power management strategies are increasingly driving these converters to operate as active power compensators. Unlike conventional approaches, these methods allow independent phase control, providing additional flexibility to enhance grid quality under unbalanced operating conditions. However, such operation typically introduces low-frequency power oscillations in the dclink, increasing losses, particularly on the dc-link capacitor. To mitigate converter lifetime degradation issues, this paper evaluates these effects through simulation and proposes a hardware-oriented methodology for capacitor selection. To validate the proposed methodology, a 3-kW prototype was built and laboratory tested.