An Improved DC Fault Protection Algorithm for MMC HVDC Grids Based on Modal-Domain Analysis

Abstract

Abstract-To detect the DC faults for MMC based DC grids using overhead line transmission, many protection methods in phase-domain have been proposed. These existing protection methods suffer from incomplete function, weak theoretical basis and sensitivity to fault resistance and noise disturbance. To overcome these shortcomings, this paper proposes an improved DC fault protection algorithm using the modal-domain approach for the MMC based overhead DC grids, which decouples interaction between positive and negative poles and mitigates the strong frequency-dependency of the characteristic impedance in phase-domain. The DC fault equivalent circuits are established in modal-domain and the fault characteristics during the initial stage are analysed. Based on the modal-domain analysis, the line-mode reactor voltage which combines fault characteristics of negative and positive reactor voltages, is employed to identify the internal faults. The zero-mode reactor voltage which enlarges the differences between faulty and healthy poles, is employed to select the faulted pole. This method is robust to fault resistance and noise with high detection speed. In addition, it is not affected by power reversal, AC faults and DCCB operation, which are validated and evaluated by simulations in PSCAD/EMTDC.

A Single-End Protection Scheme for Hybrid MMC HVDC Grids Considering the Impacts of the Active Fault Current-Limiting Control

“…To be concluded, the proposed method will not be affected by AC faults. Close-in faults are difficult to be detected [14] × 100 [28] weak √ WT mother function and sampling frequency are difficult to be selected [25] [19] √ 1000 [16] 200 More voltage transformers are required [17] 200 √ The proposed method √ /…”

“…Moreover, the impacts of fault current limiting on protection algorithms remain an unsolved problem. During DC fault analysis, the HB MMC is often simplified as a constant voltage source [17] [18] at DC side. The fault traveling wave is the main indicator to design the protection algorithm [19].…”

Comparative Study of Small-Signal Stability Under Weak AC System Integration for Different VSCs

“…The distributed capacitors in SMs relieve the requirement for the simultaneous triggering of IGBTs, making it easier to construct high DC voltage transmission. However, both TL-VSCs and HB-MMCs are vulnerable to DC faults [4] [5], limiting their application in OHL transmission systems. The HY-MMC is proposed in [3], with FBSMs and HBSMs mixed in the phase arms.…”

An Improved DC Fault Protection Scheme Independent of Boundary Components for MMC Based HVDC Grids

“…To avoid damage to power electronic devices during DC fault detection, current-limiting reactors (CLR) are implemented on the transmission lines to suppress the fault current rise rate [4]. Due to the smoothing effect of CLRs, the steep wave-front of fault traveling-wave (TW) induced from the fault point will be attenuated and the high-frequency components of DC voltage/current will be "filtered" by CLRs, which provides a boundary effect to identify internal and external faults.…”

“…Due to the smoothing effect of CLRs, the steep wave-front of fault traveling-wave (TW) induced from the fault point will be attenuated and the high-frequency components of DC voltage/current will be "filtered" by CLRs, which provides a boundary effect to identify internal and external faults. Considering this boundary effect, existing protection schemes can be divided into three categories: I) time-domain based TW methods [5]- [7], II) frequency-domain or Wavelet Transform (WT) based methods [8]- [12], III) reactor voltage based methods [4][13] [14]. Among these methods, time-domain based TW methods are ineffective to fault resistances and vulnerable to noise.…”