Small-Signal Stability of a Single Grid-Connected DFIG System

This chapter analytical derives the small-signal stability limit (i.e., the sufficient and necessary stability conditions) of a single grid-connected DFIG system in the timescale of DC voltage control. The derived stability limit establishes the analytical connections between the impact of condition of weak grid connection and the heavy loading of the DFIG generation system. It also reveals how those two affecting factors are analytically linked with the parameters setting of converter control systems of the DFIG, including the PLL. Hence, an overall view is presented about how the key factors (strength of grid connection, loading condition, and parameters setting of converter control systems) may cause the growing oscillations when the small-signal stability limit is violated. Firstly in the chapter, the full-order state-space model of a DFIG is introduced. Secondly, a simplified reduced-order model of the single grid-connected DFIG system in the DC voltage timescale is established. Based on the simplified model, the necessary and sufficient stability conditions of the single grid-connected DFIG system are derived. Finally in the chapter, an example single grid-connected DFIG system is presented.