A Noninvasive Method to Estimate the Variable Utility Harmonic Impedance

The existing noninvasive methods estimating utility harmonic impedance are usually based on the assumption that the impedance is constant during a time interval of concern. In fact, the utility harmonic impedance is variable due to various reasons such as possible short-circuit faults, grid operation changes, and capacitor switching. Thus, this paper proposes a novel method to estimate the variable utility harmonic impedance by minimizing the sum of the weighted impedance variations and the weighted variance of background harmonic voltage variations. The proposed method can track the continuous and abrupt changes of utility harmonic impedance. The effectiveness of the proposed method has been evaluated and verified through simulation and field cases.