Inverse-Impedance-Based Centralized Predictive Current Controller for $N$-Parallel Grid-Connected Converters for Circulating Current Elimination

Abstract

A constant switching frequency centralised predictive grid current controller is proposed for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N$</tex-math></inline-formula> -parallel grid-connected converters. The proposed work solves the circulating current problem even when converters of different power ratings are paralleled. The circulating current flow is eliminated by equalising the converter terminal voltages of the parallel converters. A grid equivalent model of the converter is mathematically derived using Thevenin's method to achieve the objective. The converters operate at the same power factors with their currents shared, inversely w.r.t. their line inductances/impedances. The method is flexible in applying any modulation method, without contributing to low-frequency circulating currents. Hardware experiments and software simulations validated the inverse-impedance-based current sharing among the parallel converters. Experiment results show quick redistribution of the grid current among the converters under dynamic conditions like incoming/outgoing converter scenarios. The computational requirement with the proposed scheme is independent of the number of converters in parallel. The proposed design is easy to implement and can be deployed for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N$</tex-math></inline-formula> -parallel converter systems for grid applications like interlinking converters in AC/DC grids, and plug-in type electric vehicle charging stations.