*Article* **Protection Method Based on Wavelet Entropy for MMC-HVDC Overhead Transmission Lines**

**Weibo Huang, Guomin Luo \*, Mengxiao Cheng, Jinghan He, Zhao Liu and Yuhong Zhao**

> School of Electrical Engineering, Beijing Jiaotong University, Beijing 100044, China; 15117384@bjtu.edu.cn (W.H.); 19121415@bjtu.edu.cn (M.C.); jhhe@bjtu.edu.cn (J.H.); 98930225@bjtu.edu.cn (Z.L.); 19126205@bjtu.edu.cn (Y.Z.) **\*** Correspondence: gmluo@bjtu.edu.cn or guominluo@hotmail.com; Tel.: +86-10-5168-3740

> **Abstract:** Recent technological developments in modular multilevel converter-based high-voltage direct current (MMC-HVDC) transmission systems have shown significant advantages over the traditional HVDC and two-level voltage source converter (VSC) transmission systems. However, there are a lack of studies on the protection methods for MMC-HVDC overhead lines where the protection method should be able to provide a fast and accurate response and be able to identify lightning strikes. In this paper, a wavelet entropy-based protection method is proposed. Due to the capability of revealing time–frequency distribution features, the proposed protection method combines wavelet and entropy to identify the time–frequency characteristics of different faults. Simulation results show that the proposed method can accurately and quickly determine the types of faults or disturbances with appropriate noise tolerance. In addition, the impact of the ground resistor and fault distance on the performance of the proposed method is studied.

**Keywords:** wavelet entropy; transient component; MMC-HVDC; protection

**Citation:** Huang, W.; Luo, G.; Cheng, M.; He, J.; Liu, Z.; Zhao, Y. Protection Method Based on Wavelet Entropy for MMC-HVDC Overhead Transmission Lines. *Energies* **2021**, *14*, 678. https://doi.org/10.3390/en14030678

Academic Editor: Adam Dy´sko

Received: 9 November 2020 Accepted: 27 January 2021 Published: 28 January 2021

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