Cross-Timescale Interaction Analysis Between Voltage-Control and Rotor-Speed-Control Timescales in DFIG-WTs-Dominated Power Systems

Energy storage components and control loops in Doubly Fed Induction Generator (DFIG) based wind turbines (WTs) exhibit multi-timescale characteristics. This leads to multi-timescale dynamics in DFIG-WTs-dominated power systems. Previous studies primarily focused on single-timescale dynamic mechanisms using simplified models or on interaction phenomena between control loops with full-timescale models. The cross-timescale influence mechanisms between control loops and energy storage components were neglected. This study explores the cross-timescale influence mechanism of terminal voltage control at the voltage-control timescale on the rotor dynamics at the rotor-speed-control timescale in a DFIG-WTs-dominated power system. Modal analysis is a fundamental dynamic analysis method that reveals key participating elements. It uncovers the cross-timescale influence phenomena of terminal voltage control in rotor mode. Then, the cross-timescale coupling branch of terminal voltage control to the rotor is clarified. Moreover, an equivalent circuit for terminal voltage control is established. This circuit illustrates the dynamic coupling mechanism between the terminal control equivalent inductance and the load capacitance by integrating the circuits of the DFIG and the network. Additionally, the influence of terminal voltage control on rotor mode damping is explained. The conclusions are validated through simulations in the two-machine system, the four-machine two-area system, and the IEEE 39-bus system.