Abstract
Grid impedance is an important parameter and is used to perform impedance-based stability analysis for the operation of grid-connected systems, such as power electronics-interfaced solar, wind and other distributed power generation systems. The identification of grid impedance with the help of broadband signals is a popular method, but its robustness depends strongly on the harmonic disturbances caused by non-linear loads or power electronics. This paper provides an in-depth analysis of how harmonics affect the identification of grid impedance while using broadband measurements. Furthermore, a compensation method is proposed to remove the disturbing influences of harmonics on broadband impedance identification. This method is based on exploiting the properties of the used maximum-length binary sequence (MLBS). To explain the methodology of the proposed method, the design basis for the excitation signal is discussed in detail. The analysis from simulations and a real measurement in an industrial power grid shows the effectiveness of the proposed method in compensating the disturbing influences of harmonics on broadband impedance measurements.
Highlights
The increasing decentralization of the energy system through renewable energy sources and the electrification of all aspects of daily life are leading to more and more power electronics-based devices being connected to the power grid [1]
The design of maximum-length binary sequence (MLBS) broadband excitation signal has been addressed in depth, as its inherent characteristics are the basis for the developed compensation method
It is shown that the leakage effect due to the harmonics caused by power electronic components and an inappropriate window size in the FFT transformation are a major cause of the disturbances
Summary
The increasing decentralization of the energy system through renewable energy sources and the electrification of all aspects of daily life are leading to more and more power electronics-based devices being connected to the power grid [1]. The harmonic resonance may first appear to be a power quality problem, but it is an indication of lack of system stability margin and may lead to instability and disruption of inverter operation if grid impedance or the share of inverter power further increases [3]. In [10] a method is proposed for compensating the disturbing influences of harmonics on the impedance measurement through a differential measurement by injecting harmonic currents with different phase angles This approach, only works for mono-frequency excitation signals. No published work does an in-depth analysis of influence of harmonics on the identification of AC grid impedance using broadband signals and suggests how to solve these constraints
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