Circulating Current Suppression Method for Parallel-Operated Multi-Grid-Forming Inverters Based on Adaptive Coefficient Adjustment

This paper investigates the power transfer characteristics and circulating current behavior in parallel converter systems. It highlights that impedance mismatches in the lines can lead to power coupling issues during the parallel operation of grid-forming converters. Traditional droop control strategies may to achieve precise power sharing, resulting in significant circulating currents between the parallel systems. To address these challenges, a mathematical model of parallel inverters is developed, and an improved droop control strategy based on coefficient adaptation is proposed. This strategy incorporates voltage frequency adjustment and voltage amplitude adjustment into the droop control. Different from methods that modify the droop coefficients, the proposed approach compensates for voltage frequency and amplitude without altering the original droop coefficients. Additionally, the design of adjustment coefficients enhances system flexibility and stability, effectively balancing the inherent trade-off between power sharing accuracy and output voltage drop. Moreover, it suppresses circulating currents and improves overall system performance. Finally, simulation results validate the correctness of the theoretical analysis and the effectiveness of the proposed control strategy.