Utility Harmonic Impedance Estimation Based on Sliding Difference Maxima and Improved Variable Coefficient Regression

Accurate assessment of utility harmonic impedance is a necessary prerequisite for harmonic source determination. Most of the traditional methods are based on the assumption that the utility harmonic parameters are unchanged, so that they are not suitable for the new power system with time-variation and fluctuation of utility harmonic parameters. To solve this problem, a method based on the Sliding Difference Maximum(SDM) and the improved Variable Coefficient Regression(VCR) is proposed to estimate utility harmonic impedance. This method divides the harmonic voltage or current at the Point of Common Coupling(PCC) into several relatively stable intervals by the wavelet transform-sliding difference maximum. On this basis, a VCR model of harmonic voltage and current at PCC is established, and the Adaptive Particle Swarm optimization (APSO) algorithm and generalized cross-validation method are combined to seek the optimal window width of the kernel function in the model. Moreover, utility harmonic impedance for each interval is calculated. The simulation results from MATLAB show that compared with current methods. The utility harmonic impedance can be calculated more accurately through this method when utility harmonic parameters fluctuate significantly.