Small-Disturbance Stability Limit of a Grid-Connected Wind Farm With PMSGs in the Timescale of DC Voltage Dynamics

Abstract

This paper analytically derives the small-disturbance stability limit of a grid-connected wind farm with multiple PMSGs in the timescale of DC voltage dynamics. The derived stability limit reveals the mechanism about how the dynamics of DC voltage control and the PLLs may jointly affect the small-disturbance stability of the wind farm. Flagging the impact of PMSGs by a computational function, the stability limit indicates that decreasing value of flagging function or/and increasing maximum eigenvalue of network reactance matrix implies increased instability risk. Particularly, increasing the loading conditions and number of PMSGs in the wind farm or/and the length of transmission line connecting the wind farm with main grid may make the wind farm more prone to the loss of small-disturbance stability. Although the stability limit is derived under the assumption of identical dynamics of PMSGs, the derived small-disturbance stability limit can be applied to approximately assess the small-disturbance stability of the wind farm in the timescale of DC voltage dynamics, where dynamics of PMSGs may be either similar or considerably different. The approximate small-disturbance stability assessment is simple because the assessment does not need to establish the parametric model of the wind farm.