There are serious harmonic resonance and amplification in the multi-infeed DC power network of a city

thus the premise of harmonic control and suppression is the estimation of utility harmonic impedance at DC terminals. In order to overcome the shortcomings of the existing methods

a novel method based on the criterion of minimum variance of harmonic impedance is proposed. Firstly

the actual impedance characteristics of small variance and slow change with the stability of power system operation in short sampling subinterval are considered

and the criterion of minimum variance is proposed. Then

the criterion that the impedance in short period has the minimum variance is utilized to establish the optimization function

and the norm of background harmonic is chosen as the constraint of the function. Lastly

the utility impedance which satisfies the criterion can be estimated by solving the function. The simulation cases and actual engineering scenario results indicate the proposed method can be adopted to reduce the influence of background and impedance fluctuations and solve the inaccurate estimation problem in scenario of intensive background and close magnitudes of harmonic impedance. The proposed method has lower estimation errors in multi-infeed DC systems and has reliable applicability.