Transient synchronization stability of a weak-grid connected VSC considering the interaction of outer control loops and PLL dynamics

Abstract

Since these large-scale renewable power generation (RPGs) stations are always located far away from load centres, voltage source converters (VSCs) always operate in weak-grid connected conditions, due to the long distance of transmission line and increasing capacity of RPGs. Large power disturbance of RPGs easily causes weak-grid connected VSCs (WG-VSCs) suffering from transient synchronization instability issue, which is lack of theoretical and quantitative analysis. This paper is motivated to fill this gap. By considering the dynamic interaction of outer DC voltage control, reactive power loop, and phase-locked loop (PLL), an equivalent synchronization model of a WG-VSC system is established first. Then, the mechanism of transient synchronization instability is revealed by the combination of equal area criterion and numerical integration method. Furthermore, the concept of feasible region of active power disturbance (FR-APD) is introduced for the first time. With the constructed FR-APD, the transient stability of the WG-VSC system can be confirmed. Finally, experimental results based on the RT-BOX hardware-in-the-loop platform are presented to verify the theoretical analysis.