Influence of SVC Control Parameters on DFIG-based Grid-connected Wind Farms for Sub-Synchronous Oscillation Studies

In recent years, a new type of sub-synchronous oscillation has emerged in the power system with DFIG wind farm grid-connected. And it results in large-scale wind generator off-grid accidents and seriously threatens the stability of system. Static var compensators are always installed in the wind farm grid-connected node. So it is important and urgent to study on the impact that static var compensators have on sub-synchronous oscillation. Therefore, this paper firstly analyzes the working principle and operation control characteristics of the two typical static var compensators TCR+FC and TCR+TSC. Secondly, a simulation model of DFIG wind farms is developed in MATLAB/Simulink environment. It simulates the sub-synchronous phenomenon that one DFIG wind farm has emerged in China. Finally, the action mechanism and the influence factors are analyzed that sub-synchronous oscillation occurs in DFIG wind farm system caused by different control parameter configurations of the two types of static var compensator. The results show that the TCR+TSC type static var compensator has a faster voltage response compared with the TCR+FC type. However, the sub-synchronous oscillating phenomenon would be excited in DFIG wind farm system at low wind speed, when the proportional parameter of the voltage controller is too large. At the same time, with the proportional parameters increasing, the harmonic content and harmonic amplitude of the sub-synchronous oscillation in voltage in the wind farm grid-connected node could increase, while the integral parameter doesn't cause any harm to it.