**6. Conclusions**

A more detailed understanding of the effects of different voltage and current profiles on the grid impedance requires large amounts of data, especially in the future.

Thus, a very important question is whether or not it is possible to compress data sets from impedance measurements of energy systems by using lossy compression algorithms while maintaining data fidelity. In this paper, the authors show that especially the WT (Wavelet transform) show promising results by reducing the size of the dataset in an efficient way without losing relevant information. The SVD (Singular Value Decomposition) generates almost comparable results, but need much more processing time, referring to the used programming language and computational environment. The presented approach allows of easy and effective data compression with only limited computational resources and, as a result, an increase in the number of measurements that can be stored. It is also

conceivable that the presented approach can be applied for efficient online or on-site external server data backup.

While high compression levels are useful in order to reduce the data amount for e.g., utilities, the needed level of data fidelity in the output dataset depends on the targeted application. That is why it is not the objective of this paper to create the best technique and perform on a given dataset. Lossy compression works better when the nature of the compressed data is taken into account (e.g., such as human ear characteristics in MP3). To be able to determine the limits of usability of lossy compression methods, further analyses need to be done. It must be analysed which lossy method generates the best possible outcome i.e., the maximum level of accuracy with the highest suitable compression ratio.

A comparison with lossless compression methods is also interesting. And the authors want to assess if the proposed method is suitable for on-line impedance measurement [4,5].

**Author Contributions:** M.P. modeled and validated the approaches via simulation topology, data analysis; prepared original. M.F.M. modeled the mid voltage impedance measurement system. D.S. and M.M. contributed to review and editing. F.G. developed and validated one compression method. All of them also supported the draft preparation. D.B. proofread and validate the re-submission. M.M. and D.S. provided resources and supervision. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was founded by the Federal Ministry for Economic Affairs and Energy in the course of the project "NEW 4.0—Norddeutsche EnergieWende" (Northern German Energy Transition). The support code is 03SIN414.

**Conflicts of Interest:** The authors declare no conflict of interest.
