Study on the Estimation of Utility Harmonic Impedance Based on Minimum Norm of Impedance Difference

Abstract

The existing methods for estimating harmonic impedance usually assume that harmonic impedance is constant in a measurement period. However, for a variety of practical reasons, such as the load change of power grid, utility harmonic impedance may be changed. So a reasonable hypothesis is that utility harmonic impedance is time-varying, but the variation of the impedance is not large at adjacent sampling time. Thus, this paper proposes a novel method to estimate utility harmonic impedance by taking the criterion of minimum norm of impedance differences at adjacent sampling times with a measurement period. According to the proposed criterion, an objective function is built with the norm of the harmonic impedance differences and utility harmonic voltage differences of adjacent moments. And then, the utility harmonic impedance can be obtained by minimizing the objective function. The proposed method has high accuracy even while background harmonic emission level is high and harmonic impedance of customer side is not much larger than that of utility side. The effectiveness is verified by the simulation and field cases. In the simulation, the estimation errors of most cases are within 10% and the maximum error is not exceed 16%.

Study on Harmonic Impedance Estimation Based on Gaussian Mixture Regression Using Railway Power Supply Loads

“…In addition to the above "non-intervention" method, the harmonic impedance of railway power supply system can also be obtained by the "intervention" method [22][23][24], that is, the harmonic impedance is estimated by controlling the switching of each branch or injecting harmonic current into the traction power supply system [25]. Such methods will affect the stability of the system operation, and the actual use will be limited by the on-site environment.…”