Frequency dependent grid-impedance determination with pulse-width-modulation-signals

The power quality in electrical grids is increasingly influenced by generators and loads with power electronic grid coupling. Even comparatively small harmonic currents caused by these units can lead to unacceptable high voltage harmonics at the point of common coupling (PCC) due to highly resistive resonance points of the grid impedance. Therefore, the effective grid perturbation is defined by the frequency dependent grid impedance at the PCC. In this contribution an approach is presented and analyzed to measure the frequency and time dependent grid impedance. The measured grid impedance is an important parameter for filter and controller design and can help to evaluate power quality problems of generators and loads in advance.