Bandwise Power-Synchronization Loop for Frequency Response Improvement in Grid-Forming Converters

Grid-forming (GFM) converters are prone to synchronization instability following large frequency disturbances in the external grid. The power-synchronization loop (PSL) fails to maintain grid synchronization when its droop-based power reference reaches beyond the achievable output power range. In this letter, a bandwise power-synchronization loop (BPSL) is proposed to enhance the frequency response of GFM converters. The damping power, defined as proportional to frequency variation in the PSL, is segmented by a pair of complimentary filters into low-frequency and high-frequency components to coordinate with power-limiting design. During normal operation, the proposed BPSL is equivalent to the PSL. During large disturbances, a power limiter is introduced to act on the low-frequency damping power component to provide droop-based but power-limiting frequency response. The high-frequency damping power component is completely preserved to provide adequate damping in mitigating frequency and power oscillations. Frequency response under different disturbances is verified experimentally using a hardware setup of a grid-connected GFM converter.