Abstract
The DC-link voltage control (DVC) timescale (i.e., the frequency dynamics covering converter outer controls) instabilities in wind generation have gained increased attention recently. This paper presents DVC timescale modeling and stability analysis for multi doubly-fed induction generators (DFIGs) connected to weak AC grids. A reduced-order, small-signal model of a grid-tied multi-DFIG system, designed for DVC dynamics analysis, is firstly proposed. The model allows for the dynamic interactions among the DC-link voltage control, active power control (APC), terminal voltage control (TVC) and phase-locked loop (PLL). Eigenvalue and participation factor analyses are conducted to explore the potential instabilities and correlated critical factors for such a multi-machine system. The sensitivity studies find that instability can occur at high levels of power generations or low short-circuit ratio (SCR) conditions. In addition, the dominant mode is identified to be highly related to the PLL, and its modal damping is decreased when the bandwidths of PLLs in different generators are close. Detailed model-based time domain simulations verified the analysis above.
Highlights
The last few decades have witnessed the rapid development of wind power generation around the world
The model can count the dynamic interactions between the rotor side converter (RSC) active power control (APC), the terminal voltage control (TVC) and the grid side converter (GSC) DC-link voltage control (DVC), and the phase-locked loop (PLL) of different doubly-fed induction generators (DFIGs)
The main structure of the DFIG model is inherited from the demo model in Simulink [28], and as this paper focuses on converter electromagnetic dynamics, the mechanical part, including the turbine and related controls, in the demo model is abandoned, and constant power/voltage including the turbine and related controls, in the demo model is abandoned, and constant references as converter control inputs are assumed (See Figure 1)
Summary
The last few decades have witnessed the rapid development of wind power generation around the world. A reduced small-signal model of a grid-connected DFIG, for DVC timescale stability analyses, is proposed in [11], and eigenvalue analysis implies that the PLL-related mode increases the risk of instability under a weak grid condition. The model can count the dynamic interactions between the rotor side converter (RSC) active power control (APC), the TVC and the grid side converter (GSC) DVC, and the PLL of different DFIGs. Besides, in terms of analysis, except for eigenvalue locus sensitivity studies, the participation factor curves are drawn for comparative study, which can reveal the relative impact of different controls on the system’s dominant mode in a transparent way, as well as providing guidance on controller parameter tunings for stability improvement.
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