Transient High-Frequency Impedance Comparison-Based Protection for Flexible DC Distribution Systems

Abstract

Flexible direct current (DC) distribution systems have emerged as the development trend for future distribution grids. However, these systems are vulnerable to DC faults, rapid fault identification and faulted line selection method are required to enhance the security of the entire system. A novel transient highfrequency impedance comparison based DC protection for flexible DC distribution systems is proposed in this paper. The controlindependent high frequency impedance model of power converter is also investigated. Based on this model, the proposed method identified the faulted lines by comparing high frequency impedance measurement differences. For DC bus with multiple branches, this technique minimizes the threshold calculation job, which is usually difficult to process for the transient value based protections. Strict synchronization of data is also not required for this method. The simulation model of four-terminal flexible DC distribution networks is built in PSCAD/EMTDC to verify the effectiveness of the proposed protection model. Simulation results prove that the protection is robust to fault transition resistances and the measurement noise.

An Integrated Control and Protection Scheme Based on FBSM-MMC Active Current Limiting Strategy for DC Distribution Network

“…Idc is commonly limited to zero to avoid the overcurrent in the MMCs and ensure the fault clearance. However, the fault current features detected by the protection disappear quickly under this condition, which hampers the reliable detection of the faulty line [12]. In consequence, this study limits the postfault DC current of the converter station to 1.2 p.u., i.e.…”

“…Associated with each other DCCB HSS The symmetrical monopole topology is adopted for the considered DC distribution network, which does not experience significant overcurrent during pole-to-ground faults [12]. Therefore, only pole-to-pole DC fault is studied in this paper.…”

“…14 shows the flow chart of the integrated control and protection scheme proposed in this paper. In this scheme, the start-up of FB-MMC active current limiting control is accomplished by tracking the rate of change of DC voltage [12]. After the fault occurs, the voltage of the DC network decreases rapidly.…”

“…Various fault detection methods have been studied, e.g. traveling-wave based protection [8]- [11], transient high-frequency impedance comparison based protection [12], and directional pilot protection with over-current criteria [13], etc. However, these methods can only detect the faulty line and the fault clearance remains unclear.…”

Bad Data Detection Algorithm for PMU Based on Spectral Clustering

“…P HASOR measurement units (PMUs) have become an important mechanism used in the ubiquitous electric of the Internet of Things to achieve state perception, due to their rapidity, synchronism, and accuracy [1]. Furthermore, PMUs can provide real-time phasor time data for critical power system applications such as remedial action schemes, oscillation detection, and state estimation [2] - [6]. Up to 2018, approximately 3000 PMUs have been installed and put into operation in China, covering the majority of 220 kV and above substations, power plants, and grid-connected renewable energy collections [7].…”