Small Signal Synchronous Stability Analysis of Grid-Connected VSC in Weak Grid

Abstract

This paper investigates the small signal synchronization stability problem of grid-connected converter based on phase-locked control in weak grid. Firstly, with the objective of mechanically revealing the synchronization characteristics of the grid-connected converter, a Heffron-Phillips dynamics model is established for the analysis of the synchronization stability of the grid-connected converter by analogizing its synchronization dynamics with that of the traditional synchronous machine. By referring to the traditional low-frequency oscillation analysis idea of power system, the damping of synchronous oscillation mode dominated by phase-locked loop (PLL) is divided into two parts: the inherent damping component of PLL itself and the additional damping component introduced by complex control coupling in weak grid. Then the synchronous stability mechanism of the grid-connected converter in weak grid is revealed from the perspective of the damping characteristics. And from the perspective of the influence of the inherent or additional damping components, the influence of the controller parameters on the synchronous stability of small signal is investigated. The results of this paper clearly reveal the mechanism of synchronous instability of grid-connected converter in weak power grid, and indicate the way for the subsequent synchronous stability control.