## 2 Characterization and Modeling of the Fault Ride-Through Process in Doubly Fed Wind Turbines
### Analysis of Core Control Parameters for Fault Transient Processes  
In the parameter identification study of the structured model of a new energy unit, the reasonable selection of the identification parameter set is the key to ensuring the model's accuracy and identification efficiency. About the topological characteristics and dynamic response mechanism of the structured model of the new energy unit in this paper, the parameter identification needs of non-critical control modules can be systematically excluded. On the one hand, the time constants of the mechanical side control and FM inertia control modules are generally more significant than the millisecond dynamic process of the fault ride-through process, and their parameters have lower coupling to the transient characteristics; on the other hand, the active/reactive control module under normal operating conditions will be forced to block during faults, and its parameter impact on the fault response characteristics is negligible. The PI parameters of the inverter inner-loop current control module adopt the voltage feedforward decoupling strategy so that its PI parameters have negligible influence on the fault response characteristics. In addition, although the mechanical side control module can characterize the mechanical dynamics of the wind turbine, its second-time scale is significantly decoupled from the millisecond transient process of grid faults, so it is also not required to be included in the identification system.  
From the analysis of the structured model fault ride-through control in the previous section, it can be seen that the fault ride-through active and reactive power control module, as the core control link of the model in the case of grid fault perturbation, the three-segment control strategy of the fault ride-through and its key control parameters directly determine the dynamic response characteristics of the unit. Hence, determining the fault ride-through control strategy and the control parameters to be identified is the basis for guaranteeing the accuracy of the identification simulation results. Therefore, determining the control strategy and control parameters to be recognized in the fault ride-through control process is the basis for guaranteeing the accuracy of the identification simulation results, and the control parameters of the whole fault ride-through process are shown in Table 3:  
The initial active power and active current and the initial reactive power and reactive current in the structured model are the input reference values during normal control operation; therefore, analyzing the mathematical expressions of the fault ride-through three-segment control, it can be seen that the initial parameters \(P_{0}\), \(Q_{0}\), \(I_{00}\), and \(I_{00}\) have no influence on the power and current changes during the fault period. In addition, the structured model fault ride-through conditions can be divided into four typical scenarios: symmetrical low/high fault ride-through and asymmetrical low/high fault ride-through. Inorder to comprehensively validate the applicability of the model and the fault ride-through control identification to different types of fault conditions, it is necessary to analyze the ride-through characteristics of different types of faults in a differentiated manner and to identify the fault ride-through three-segment control strategy and the control parameters of the faults under the various types of faults, respectively.