Analytical Assessment of Reactive Power Support Capacity for DFIGs Under Voltage Drop Failure

Since the reactive power support capacity of the doubly-fed induction generator (DFIG) during grid failures can be scheduled within a certain range, DFIGs are used as an effective and controllable reactive power source to support the AC grid voltage. However, the nonlinearity of the power flow equations in wind farms and the uncertainty of the reactive power range of DFIGs limit the accurate assessment of the reactive power support capacity of DFIG-based wind farms. To this end, this paper proposes a reactive power support capability evaluation method considering the internal and external constraints of DFIG operations. By focusing on the impacts of the rotor current and the coupling between the terminal voltage and reactive power on the allowable reactive power support capacity of DFIGs, analytical constraints of allowable reactive power of DFIGs under voltage drop are analyzed. At last, with the time domain simulation analysis, the allowable reactive power range of DFIGs considering internal and external constraints is verified.