Harmonic impedance measurement using voltage and current increments from disturbing loads

A device has been developed to measure the harmonic impedances of power network by using harmonic voltage and current increments at the point of common coupling between the network and a disturbing load. The key problem in the implementation of the method is the synchronization of phasors sampled asynchronously and at different times. This kind of synchronization is linked to the frequency measurement. A small error in the frequency will cause a great deviation of the impedance measurement. A formulation is given here to evaluate the error on the impedance in each individual measurement (event), and a statistical method is proposed to achieve a relatively high accuracy in the source impedance estimation. Laboratory and field tests results are both discussed as well as verified with the harmonic emission level estimation of the disturbing load.