## 5 Conclusions  
In this study, the working principle of the DFIG system was introduced, and the fault current characteristics of the DFIG were theoretically analyzed. The correctness of the theoretical calculations for the fault current of the DFIG stator was verified through the simulation results. Furthermore, it can be concluded that during the fault period, the fault current of the DFIG stator exhibits frequency offsetting, and the frequency offset of the fault current is closely related to factors such as the depth of the voltage dips and the crowbar circuit. Therefore, by adopting a DVR-based SMES system to compensate for the voltage dips of the DFIG in practical applications, the stator voltage of the DFIG can be compensated to a rated voltage of 0.69 kV, and the frequency offset of the fault current can be significantly improved to a rated frequency of 50 Hz. The simulation results using the RTDS platform show that during different-type faults, the DVR-based SMES can effectively compensate for the fault voltage of the 35 kV line. Additionally, during an 80% depth three-phase-to-ground fault, the frequency of the fault current, which fluctuates between 46-54 Hz, can be stabilized at 50 Hz. During a 70% depth single phase-to-ground fault, the frequency of the fault current, which fluctuates between 47-53 Hz, can be stabilized at 50 Hz. Additionally, with a DVR-based SMES to compensate for the fault voltage, the output power of the DFIG can be maintained at a normal power value during the fault. Therefore, this method can achieve the fault ride through and improve the frequency of the DFIG fault current. Additionally, future research should focus on how to reduce the cost of the DVR-based SMES device by making full use of DVR-based SMES or improving the design of the DVR-based SMES device.  
Figure 15: Comparison of the DFIG output power an adopted DVR-based SMES at a voltage dip depth of 70%; an adopted DVR-based SMES at a voltage dip depth of 20%; crowbar circuit protection at a voltage dip depth of 70%; and crowbar circuit protection at a voltage dip depth of 20% when the single phase-to-ground fault occurs.  
**Author Contributions:** Conceptualization, methodology, investigation, formal analysis, L.L.; methodology, investigation, formal analysis, Y.L.; conceptualization, methodology, formal analysis, J.N.; conceptualization, methodological, methodological, methodology, formal analysis, J.N.; conceptualization, methodology, investigation, formal analysis, J.H.; conceptualization, methodological, methodology, investigation, H.L.; investigation, formal analysis, supervision, B.L.; investigation, formal analysis, writing--review and editing, supervision, C.L.; methodology, visualization, writing--original draft preparation, writing--review and editing, Y.C. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded in part by the Science and Technology Research Program of the State Grid Ningxia Company. (B329 DK210003) and funded in part by the Natural Science Foundation of Ningxia (2023 AAC03838).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.