Dynamic Frequency Characteristic Of Power Generation System With Controlled Inertia And Integrated Control

The virtual inertia control of variable speed wind turbines, effectively avoid weakening the system inertias and eliminate the negative impact on frequency stability. However, different from the inherent inertias of conventional generators,virtual inertias of wind turbines is variable. Therefore, considering high renewable power penetration, the virtual inertias of regional network will be regarded as a new adjustable operating parameter for the improvement of the grid dynamic stability.This paper mainly studies the impact on transient angle stability and power oscillation caused by virtual inertia, and the main research results are as follows:Firstly, the mathematical models of DFIG are established, and the working principle and the inertia control strategy are also analyzed. Based on this, the system models of DFIG with the virtual inertia control are built by using DIg SILENT/Power Factory software, which lays the foundation for the following work.Secondly, with the aid of extended equal area criterion, the impact on the transient angle stability of the interconnected system caused by virtual inertia is analyzed. The results show that the transient stability of the system is improved when the virtual inertia reduces the angle acceleration of synchronous generators of which the power angle swings forward.Thirdly, based on the linear state equation derived from two-area generation system, the system inertia is considered as an adjustable control parameter, thus its impact on power oscillation is analyzed. Then, an integrated inertia control strategy for the two-area generation system is proposed to enhance the dynamic stability using controlled inertias of wind turbines. This control strategy achieves the inertia support and damping control for power grid by dynamically changing the virtual inertia.Fourthly, a two-area network with high wind penetration is established to validate the proposed control strategy. The simulation results show that the proposed control strategy can give inertial support for power grid, prevent frequency beyond the limits, and speed up the frequency recovery, avoid the occurrence of frequency’s secondary collapse. In addition, the integrated inertial control strategy also effectively improves the system damping, and realizes the purpose of rapid inhibition of power oscillation.