A Differential Pilot Protection Scheme for MMC-Based DC Grid Resilient to Communication Failure

Abstract

Primary single-end line protection strategies of MMC HVDC systems are difficult to make a tradeoff between fast detection speed and high reliability. To improve reliability, the pilot protection schemes based on communication and data exchange can be adopted. However, the communication-based schemes suffer from potential communication failure problems, such as data error, data loss and time synchronization error. To avoid blocking of protection devices during communication failures, a resilience-oriented differential pilot protection method is proposed in this paper. To address the problem of synchronization error, a startup element based on the multiresolution morphological gradient (MMG) of traveling wave is proposed. For the problems of data error and data loss in communication, the sampled data are preprocessed by the morphological filtering (MF). And the correlation of traveling waves is used to identify the internal and external faults; the ratio of the morphological gradient of pole voltages is adopted to discriminate the faulty poles. A four-terminal MMC based DC grid model is built in PSCAD/EMTDC interfaced with the optical fiberbased communication system built in MATLAB/Simulink. The simulation results show that the protection scheme can effectively identify the faults against serious communication problems of 1% bit error rate and 5% data loss.

DC Fault Protection Algorithms of MMC-HVDC Grids: Fault Analysis, Methodologies, Experimental Validations, and Future Trends

“…The sensitivity requires the protection devices to accurately detect any internal faults, regardless of fault types and fault resistances [35], e.g., the pole-to-pole (PTP) and the pole-toground (PTG) faults. Considering the coupling of the faulted and healthy poles, some methods have been proposed to discriminate the faulted poles, e.g., the integration of the change of pole voltages [31], the zero-mode component based methods [36], the morphological gradient based methods [37].…”

Fault detection method for flexible DC grid based on current limiting reactance voltage variability

“…Therefore, designing a reliable fault detection method is one of the important challenges facing flexible DC grids [10]. Existing fault protection for DC grids can be categorized into single-ended quantity protection [11][12][13][14][15][16][17][18] and double-ended quantity protection [19][20][21][22][23][24] based on the selection of electrical quantities.…”

MMC‐HVDC AC side line protection based on positive sequence fault component current ratio

“…At present, the research on relay protection technology of MMC-HVDC transmission line mainly includes voltage and current sudden variable protection [15,16], pilot protection [17][18][19][20] and traveling wave protection [21][22][23][24]. A fault detection technique based on initial current burst is proposed in [15], which only depends on the information from the local terminal and does not need the communication channel.…”

“…The energy ratio of forward and backward traveling waves is calculated in [22,23], which eliminates the negative influence of the frequency correlation characteristics of subsequent traveling waves and line parameters. In [24], the similarity between local forward traveling wave and reverse traveling wave is calculated, and the morphological filtering algorithm is applied to data preprocessing. Although the above traveling wave protection has the advantage of fast response, they need high sampling frequency and are easily affected by transition resistance and noise.…”