Modern distribution grids face mounting challenges from the integration of distributed energy resources, electric vehicles, and unequal single-phase loads, which create three-phase voltage imbalances and destabilize DC-link voltages in interconnection systems. These imbalances propagate through power conversion stages, introducing low-frequency ripples into the common DC bus and causing harmful neutral-point potential drift in capacitor banks.
Researchers have developed an advanced cooperative control framework for energy-storage-based systems equipped with three-level Buck–Boost converters. The innovation lies in decomposing the DC-side modulation signal into two independent components: a common-mode duty cycle and a differential-mode duty cycle. The common-mode component manages overall power exchange to maintain stable DC bus voltage and suppress low-frequency ripple generation. Simultaneously, the differential-mode component regulates the duty cycle asymmetry between upper and lower converter stages, enabling precise capacitor charge distribution and neutral-point potential equilibration.
The strategy first establishes the mathematical coupling relationship between AC-side power fluctuations under unbalanced conditions and resulting DC-side voltage dynamics. This analysis reveals how unbalanced loads introduce oscillations at twice the grid frequency into the DC bus, a mechanism often overlooked in conventional control designs. The proposed method separates these coupled phenomena into tractable subproblems, each addressed by dedicated control loops.
Simulation validation demonstrates robust performance under demanding conditions. When subjected to power step disturbances, the system maintained DC bus voltage near the 800 V nominal setpoint while reducing neutral-point voltage deviation from approximately ±10 V oscillations to within ±1 V—a tenfold improvement. This enhanced voltage stability directly benefits connected equipment, extends component life, and improves the overall quality of power supplied to downstream loads.
The method represents a significant step toward resilient, distributed energy networks capable of accommodating variable renewable generation and flexible loads without sacrificing voltage quality or control performance.
