Weakly Time-Variant SOGI-Based Frequency Derivative Estimator

Recent works revealed the inherent periodically-time-variant property of the second-order generalized integrator-based frequency-locked loop (SOGI-FLL). This work further finds that this property affects the frequency derivative estimation of SOGI-FLL under time-variant frequency. A weakly time-variant frequency derivative estimator is, thus, given to overcome this problem. Besides, this estimator reduces the transient deviation of the frequency derivative during the voltage sag and phase jump. It is theoretically proved that this weakly time-variant idea shrinks the variation range of the coupled time-variant coefficient between the frequency derivative and amplitude/phase error. Comparative tests are given to validate the claims.