Complex Frequency Locked Loop for Estimations of RoCoV and Frequency

Recently, the concept of complex frequency (CF) has been introduced to unify the rate of change of voltage (RoCoV) and angular frequency, facilitating the development of CF-based droop control. However, in conventional grid synchronization, the amplitude of the measured bus voltage is typically computed in an open-loop fashion, and RoCoV is not estimated. In this letter, a complex frequency-locked loop (CFLL) is proposed to estimate the CF including both RoCoV and frequency information. In the proposed CFLL, RoCoV is estimated using closed-loop feedback, resulting in improved performance compared to conventional discrete-time differentiation and synchronous reference frame phase-locked loop (SRF-PLL) based methods. The dynamic response of the RoCoV also becomes symmetric with that of the frequency estimation. Experimental results validate the effectiveness of the proposed CFLL.