A new algorithm for calculating utility harmonic impedance

•Estimation accuracy is improved when harmonic impedance ratio is about 1.•The idea is the weak correlation of harmonic current fluctuation.•This algorithm has a strong ability to resist non-stationary signal interference. In engineering, it is very valuable to estimate the utility harmonic impedance of a point of common coupling (PCC). However, the existing methods usually assume that the customer harmonic impedance is much larger than the utility harmonic impedance, if not, the estimated accuracy is hard to meet engineering requirement. Unfortunately, in modern power grid, due to the influence of filters or reactive compensation capacitors installed on the customer side of a PCC, the above assumption is no longer valid. This paper proposes a new algorithm to overcome this problem, the proposed algorithm can get a fairly good estimated result while the amplitude of utility harmonic impedance is approximately equal to the customer harmonic impedance. In this algorithm, firstly, the amplitude of utility harmonic impedance is calculated by using the weak correlation of the fluctuation of the harmonic sources on both sides of a PCC, and the impedance angle can be obtained through minimizing background harmonic fluctuation energy. Simulation and field case verify the effectiveness.