Frequency control for weak AC grid connected to wind farm and LCC-HVDC system: Modeling and stability analysis

Interconnection of DFIG-based wind farms with LCC-HVDC is challenging for very weak AC systems. This work focuses on establishing a modeling and control design framework to analyze frequency dynamics in such systems. To that end, an averaged model of the DFIG-based wind farm connected to LCC-HVDC system has been developed where grid frequency control is used to regulate the HVDC rectifier firing angle. This paper analyzes the effect of low Effective Short Circuit Ratio (ESCR) and the Effective DC Inertia Constant Hdc on the stability of the system. A systematic design process of the frequency controller parameters reveals a negative interaction between the generator speed-HVDC PLL-frequency controller mode and the DFIG-GSC controller mode.