Abstract
This article presents the grid-forming control (GFC) for doubly-fed induction generator (DFIG)-based wind farm to enhance the stability of line-commutated converter (LCC) based high voltage direct current (HVDC) transmission system. GFC is a grid friendly control strategy to build or follow the grid voltage and provide inertia support for power grid. The GFC for DFIG can not only improve the stability of HVDC sending-terminal system, but also reduce the dependence of synchronous generator (SG) in HVDC sending-terminal system. Impedance analysis is used to analyze the stability of HVDC sending-terminal system. The impedance modeling process of the GFC for DFIG is introduced in detail. Based on the impedance analysis, the GFC for DFIG shows the better stability than the conventional vector control (VC) for DFIG in HVDC sending-terminal system. When the capacity of SG decreases and transmission line impedance increases, the GFC for DFIG can keep stable, while the VC for DFIG will lose the stability in HVDC sending-terminal system. Vector graph of impedance characteristic is applied to illustrate the mechanism of instability. The time domain simulations are presented to verify the impedance analysis. Moreover, the simulation in islanded condition is also given to illustrate the stability and effectiveness of the GFC for DFIG.
Highlights
Line-commutated converter (LCC) based high voltage direct current (HVDC) transmission systems have been widely utilized worldwide
Based on the analysis above, the following conclusions can be obtained: 1) As the capacity of synchronous generator (SG) decreases or the short circuit ratio (SCR) decreases, the impedance magnitude of SG will increase, which may lead to the instability in the HVDC sending terminal within the sub-synchronous frequency range, when doubly-fed induction generator (DFIG) wind farm is controlled under vector control (VC)
This article has discussed the grid-forming control for DFIG to enhance the stability of the line-commutated converter (LCC)-HVDC sendingterminal system
Summary
Line-commutated converter (LCC) based high voltage direct current (HVDC) transmission systems have been widely utilized worldwide. This article presents the GFC for DFIG-based wind farm with connecting LCC-HVDC and analyzes the stability of HVDC sending-terminal system. The contributions of this manuscript can be concluded as: 1) presenting the GFC for DFIG to improve the stability of HVDC sending-terminal system, and building the impedance model of the GFC for DFIG; 2) based on the impedance model, analyzing the stability of HVDC system with considering the capacity and transmission line of SG; 3) the GFC for DFIG can be applied to both grid-connecting mode and islanded mode, it can build and support grid voltage, but decrease the dependence on the SG. The detailed analysis based on the impedance model will be illustrated
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