Asymmetric Matrix Control Strategy for Suppression of Charging Mode Resonances in Grid-Forming Energy Storage Converters

Grid-forming energy storage converters (GFM-ESC) are essential for stabilizing power electronic-based grids owing to their voltage and frequency support capabilities. However, current research primarily focuses on the discharging mode of GFM-ESC, while grid-supporting characteristics in the charging mode remain underexplored. This paper firstly identifies a phenomenon that the GFM-ESC is stable in the discharging mode but exhibits low-frequency resonances in the charging mode. To investigate the instability mechanism of this oscillation, a reduced-order small-signal impedance model for GFM-ESC is developed, revealing that the current matrix, resulting from the dynamics of the reactive power loop, is the primary factor causing instability. Therefore, this paper proposes an asymmetric matrix control strategy based on q-axis voltage feedforward, which optimizes the reactive power loop to reshape the current matrix, thereby counteracting its negative impact on stability and ensuring stable operation across different modes. Finally, simulation and experimental results validate the correctness and effectiveness of the proposed control strategy.