Multi-terminal Hvdc system with offshore wind farms under anomalous conditions: Stability assessment

Droop control is widely adopted to control Multi-Terminal high-voltage Direct Current (MTDC) systems with offshore wind farms. During permanent faults, the faulty line should be isolated promptly to preserve a high reliability of the MTDC system. This paper examines the MTDC system performance following a faulty line outage. This study aims to identify the outage types that may lead to a complete loss of system voltage stability and the outages that may have a secondary effect on the system. Moreover, strategies for dealing with outages that may lead to a complete shutdown of the system are also presented. Furthermore, the ranges of droop gains' values that can be employed following fault occurrence to preserve system transient stability are studied. Different scenarios are explored during faulty conditions such as surplus and sparsity of wind power, line overcurrent, outage of lines connected to wind farms, and outage of lines connected to AC grids to validate this study.MATLAB/Simulink platform has been employed to elucidate the presented concept.Qatar National Research FundScopu

A directional protection technique for MTDC networks

This paper suggests a new protection algorithm for a multi-terminal direct current (MTDC) networks. The current values and directions at each bus connecting more than one line are determined. The measured values of line currents are used to detect faulty conditions based on a specific threshold value. The faulted line is identified using the current direction through each line during a fault. For lines linking buses that connect multiple lines, simple communication system is required between the ends of these lines to identify an internal fault. The communication time is compensated due to the fast decision. Communication between buses is not required during normal conditions; therefore, the communication task is simplified. Simulation results show that the proposed algorithm is effective in protection of MTDC.Scopu

A differential protection technique for multi-terminal HVDC

This paper presents a technique for differential protection of Multi-terminal High Voltage Direct Current (MTHVDC) transmission lines. The proposed technique depends on the electrical current data at both ends of each line section. Discrete Wavelet Transform (DWT) is used to detect DC faults as well as filter out the high frequency transients superimposed on the current signals. An operating signal and a restraining signal are used in this technique to discriminate between internal faults and external faults through their ratio in each section of the MTHVDC. The operating and restraining signals depend on energy contents of the de-noised current signals at both ends of each line section. MTHVDC modeling and relay design are carried out in the MATLAB environment. The results demonstrate the high reliability of the proposed relay in the zonal protection of MTHVDC. All rights reserved.This publication was made possible by NPRP grant NPRP 4-941-2-356 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors.Scopu

A Droop Control Design for Multiterminal HVDC of Offshore Wind Farms With Three-Wire Bipolar Transmission Lines

Converting existing ac transmission lines to an extended multiterminal three-wire bipolar HVDC system can be considered a cost-effective way to interconnect dispersed offshore wind farms to onshore ac grids instead of building new bipolar HVDC systems. To automatically coordinate between different converters in a multiterminal HVDC (MTDC) system, droop control techniques have been adopted as an effective means without the need for fast communications between units. The droop control design is mainly dependent on the line resistances. This paper shows that the equivalent resistance of a three-wire bipolar system changes based on the operational mode. The modification to droop control design of an MTDC equipped with a three-wire bipolar system is then presented to tackle this resistance variation with the operating condition. Two types of MTDC systems are considered in this work, namely, radial parallel and meshed parallel systems. Different simulation studies have been conducted to validate the results of the presented analysis.QNRF NPRP 4-941-2-35