Abstract
Recent works have shown that phase-locked loop (PLL) synchronized wind turbines (WTs) suffer stability issues when integrated into weak grids. However, most of the current studies are limited to a single machine case, the interactions among the WTs are usually overlooked. This paper studies the stability of multiple doubly-fed induction generators (DFIGs) that are connected in parallel to a weak AC grid. A state space model of a two-DFIG system is firstly presented. Subsequently, eigenvalue sensitivity analysis shows that instability can occur at low short-circuit ratio (SCR) or heavy loading conditions. Meanwhile, participation factor analysis implies that the unstable mode is primarily induced by the interactions between the PLLs of the two WTs. Further, to make out how the PLLs interact to cause instability, a reduced-order model is proposed for analysis simplicity, and an explanation in terms of transfer function residue is given for illustration. Detailed model-based time domain simulations are conducted to validate the analyses’ results.
Highlights
Wind power generation has witnessed a prosperous development over the last two decades.In many parts of the world, the rich wind energy resources are located far from the load centers, resulting in wind farms being integrated into a weak AC grid with a long transmission line
This section utilizes participation factor analysis to explore the correlated by the associated controls, e.g., DC-link voltage control significantly contributes to the dynamic state state variables and controls to system of this critical sectionmodes
This work studies the synchronization stability of a system that is composed of two doubly-fed induction generators (DFIGs) that
Summary
Wind power generation has witnessed a prosperous development over the last two decades. The partial-VSC interfaced doubly-fed induction generator (DFIG) is found to suffer similar instabilities due to PLL, except for the full-VSC based permanent magnetic synchronous generator (PMSG) [8] Alternative synchronizing techniques, such as power synchronization control [9] and virtual synchronous control [10], are proposed to enhance the adaptability of VSC-based devices into low SCR weak grids to overcome the limitation of PLL.
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