A Unified Grid-Forming Structure with Power Control Capability for DFIG Wind Turbines

In doubly-fed induction generator wind turbines (DFIG-WT), both the stator and grid-side converter can affect the voltage at its output terminal, making it more complicated to realize grid-forming control than Type-IV wind turbine and energy storage system. Current research on grid-forming DFIG-WT focuses on methods such as power synchronization control, VSG control without inner-loop, and dc-link voltage synchronization control. However, less consideration was given to reasonable cooperation between both sides to achieve better overall voltage source characteristics, and mode switching was inevitable to implement frequency dead zone and power limit control, which is commonly required in wind power generation. This paper analyzes the requirements of grid-forming control for DFIG-WT, and proposes a unified grid-forming control scheme that can achieve the aforementioned frequency dead zone and fast power control capability without mode switching, as well as providing desired inertia response and frequency regulation feature. Numerical simulation is carried out and validation result is presented.