Current Saturation Ratio-Based Hybrid Synchronization Control of Grid-Forming Converters

Grid-forming (GFM) converters utilizing hybrid synchronization control (HSC) incorporate both power-synchronization loop (PSL)- and phase-locked loop (PLL)-based frequency components in the synchronization loop. However, existing implementations of HSC do not consider the physical current limits of GFM converters, are designed to only cater to specific types of grid disturbances, and exhibit inaccurate power setpoint tracking. In this letter, a current limit-informed HSC method is proposed to overcome these issues. The PSL and PLL components are weighted according to the current saturation ratio (CSR) of the current limiter, as a proxy measure for the severity of a disturbance. In this way, the proposed method not only synergizes with current limiting control of GFM converters, but also works generally for any disturbance which activates the current limiter. Additionally, it tracks the active power setpoint accurately during unfaulted steady states, which also implies that a larger proportional gain can be used in the PLL, improving the design flexibility and dynamic performance. Experimental results demonstrate the enhanced performance of the proposed method over the PSL and existing HSC methods during grid frequency drops and voltage sags. The stability of the proposed method under weak grid conditions is also experimentally verified.