Investigation on sub-synchronous oscillations in DFIG-based transmission system based on improved complex torque coefficients method

Abstract

The complex torque coefficients (CTC) method has been widely adopted to investigate the conventional sub-synchronous oscillation (SSO) issues. However, the application of the CTC method is limited when large-scale wind power generations are integrated into power systems. Therefore, in order to overcome the disadvantages of the CTC method on the aspects of frequency scan and stability determination, this paper proposes an improved CTC method based on the shaft system modal decoupling and small-signal self-excitation theory. The improved method is demonstrated and validated through the IEEE first benchmark power system (FBMPS). By establishing the small-signal model of the series-compensated DFIG-based transmission system, the proposed method is applied to examine the SSO in a grid-connected DFIG system. Moreover, the impacts of different parameters on the electrical damping characteristics of the system are deeply analysed. In addition, an effective VSC control strategy for suppression of the SSO in series-compensated DFIG-based transmission system is proposed.

Keywords

• damping
• torque
• wind power plants
• asynchronous generators
• power generation control
• power system stability
• power grids
• power transmission control
• VSC control strategy
• electrical damping characteristics
• IEEE first benchmark power system
• SSO suppression
• subsynchronous oscillations
• grid-connected DFIG system
• series-compensated DFIG-based transmission system
• small-signal self-excitation theory
• shaft system modal decoupling
• improved CTC method
• stability determination
• frequency scan
• large-scale wind power generations
• improved complex torque coefficients method