Abstract
In this paper, we developed the small-signal state-space (SS) model of hybrid multi-terminal high-voltage direct-current (HVDC) systems and fault localization method in a failure situation. The multi-terminal HVDC (MTDC) system is composed of two wind farm side voltage-source converters (VSCs) and two grid side line-commutated converters (LCCs). To utilize relative advantages of the conventional line-commutated converter (LCC) and the voltage source converter (VSC) technologies, hybrid multi-terminal high-voltage direct-current (MTDC) technologies have been highlighted in recent years. For the models, grid side LCCs adopt distinct two control methods: master–slave control mode and voltage droop control mode. By utilizing root-locus analysis of the SS models for the hybrid MTDC system, we compare stability and responses of the target system according to control method. Furthermore, the proposed SS models are utilized in time-domain simulation to illustrate difference between master–slave control method and voltage droop control method. However, basic modeling method for hybrid MTDC system considering superconducting DC cables has not been proposed. In addition, when a failure occurs in MTDC system, conventional fault localization method cannot detect the fault location because the MTDC system is a complex form including a branch point. For coping with a failure situation, we propose a fault localization method for MTDC system including branch points. We model the MTDC system based on the actual experimental results and simulate a variety of failure scenarios. We propose the fault localization topology on a branch cable system using reflectometry method. Through the simulation results, we verify the performance of fault localization. In conclusion, guidelines to select control method in implementing hybrid MTDC systems for integrating offshore wind farms and to cope with failure method are provided in this paper.
Highlights
Wind energy is poised to be an important component for a diversified energy portfolio in power networks [1]
To embrace wind energy sources for various locations and to provide bulk wind power for various system operators, the multi-terminal high-voltage direct-current (HVDC) (MTDC) system technologies are highlighted for wind farm integration [4]
This paper provides small-signal state-space (SS) model of a hybrid MTDC system featuring wind farm side voltage-source converters (VSCs) and grid side line-commutated converters (LCCs), and root locus analysis using the SS model
Summary
Wind energy is poised to be an important component for a diversified energy portfolio in power networks [1]. To integrate offshore wind farm and onshore network over a long distance, high-voltage direct-current (HVDC) technology has been proved to provide many advantages on its ac counter part [3]. High temperature superconducting (HTS) cables have many strong points which are a compact size, have capabilities of transmitting a large amount of electric power, and less construction cost than that of conventional cable. According to these positive aspects of HTS cable, HTS cable would be a suitable cable for the future power grid, and the future power grid would be called high-voltage direct-current (HVDC). HTS cable is installed to connect between two substations including transmission and distribution bus
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