A Fixed-Length Transfer Delay Based Adaptive Frequency-Locked Loop for Single-Phase Systems

This letter presents an adaptive frequency-locked loop (FLL) with fixed-length transfer delay units for single-phase systems. By analyzing the relationship between the grid voltage and its transfer delay signals, a linear regression model of the grid voltage is established. Accordingly, a transfer delay based adaptive FLL (TD-AFLL) is proposed. A mathematic proof indicates that the proposed TD-AFLL can reject both phase offset errors and double-frequency oscillatory errors. Thus, the grid voltage parameters can be estimated accurately, even when the frequency drifts away from its nominal value. Moreover, fast dynamics of the TD-AFLL are achieved due to the transfer delay structure. Experiments verify the effectiveness of the proposed method.