Analysis of DFIG Fault Short-circuit Current Considering Crowdbar Unloading Circuit Switching

The short-circuit current is one of the important bases for analyzing the dynamic characteristics of doubly-fed fans, and it is of great significance to find the expression of the short-circuit current under the consideration of crowdbar unloading circuit input and cut-out. Based on the transient mathematical model of doubly-fed fan, this paper firstly analyzes the mathematical relationship between rotor voltage and rotor current during the fault period, forms the non-chiral second-order differential equations about the rotor current, deduces and calculates the stator and rotor currents during the fault period of the doubly-fed fan, and analyzes the transient components contained in the stator and rotor short-circuit currents. On this basis, the short-circuit current response of the DFIG is further investigated after the crowbar unloading circuit is put in and removed during the fault period, and the response characteristics are analyzed to be affected by the control parameters and the crowbar casting and cutting time. Finally, an electromagnetic transient simulation model reflecting the sequential switching characteristics of the wind turbine control system is built on the PSCAD/EMDTC platform to verify the correctness of the stator short-circuit current expression under short-circuit fault.