# High Voltage Ride through Strategy of Wind Farm Considering Generator Terminal Voltage Distribution
## 5 Simulation and Analysis
### Simulation Result and Analysis  
With a DC blocking fault occurring at 1 s, then the sending end AC busbar voltage swells rapidly, due to the surplus of reactive power, which exceeds the normal operating range allowed by the wind farm, and the wind turbines enter the HVRT process. According to the specifications of HVRT technology in various countries, wind turbines are required to keep operation when the generator terminal voltage is lower than 1.1 p.u. [25]. Therefore, the value of the generator terminal voltage determines whether the wind turbine is able to ride-through successfully. Taking into account the operational safety of all wind turbines in the wind farm, the voltage swell index (VSI) is proposed to calculate the average ratio of each generator terminal voltage to 1.1 p.u., which is used to measure the performance of the HVRT strategy. The calculation formula of VSI is shown in Equation (16). Similarly, according to the specifications of HVRT technology in various countries, wind turbines are required to keep operation for a certain time when the generator terminal voltage is higher than 1.1 p.u. [24]. Ride-through time (RRT) index was also proposed to measure the performance of the HVRT strategy. \[\text{VSI}=\frac{\sum\frac{\mu_{\text{I}}}{\prod_{\text{I}}}}{n} \tag{16}\]  
Taking the grid-connection node as the control target of the synchronous condenser, the generator terminal voltage variation curves of the wind turbines on the three collection lines are shown in Figure 14, respectively, and the partial of generator terminal voltage variation curves during HVRT are shown in Figure 15, respectively. HVRT indicators are shown in Table 4.  
Adopting the proposed strategy, the generator terminal voltage variation curves of the wind turbines on the three collection lines are shown in Figure 16, respectively, and the partial curves of generator terminal voltage variation during HVRT are shown in Figure 17, respectively. HVRT indicators are shown in Table 5. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Collection Line** & **VSI** & **RTT/ms** \\ \hline Line 1 & 1.041 & 59.838 \\ Line 2 & 1.074 & 83.855 \\ Line 3 & 1.104 & 84.450 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: HVRT indicators, considering the grid-connection node as the control target. \begin{table}
\begin{tabular}{l l} \hline \hline
**Description** & **Value** \\ \hline Rated capacity & 3 MW \\ Stator impedance & 0.023 p.u. \\ Stator inductance & 0.18 p.u. \\ Rotor impedance & 0.016 p.u. \\ Rotor inductance & 0.16 p.u. \\ Magnetizing inductance & 2.9 p.u. \\ Wind speed (constant) & 11 m/s \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Parameters of DFIG. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Collection Line** & **VSI** & **RTT/ms** \\ \hline Line 1 & 1.004 & 29.712 \\ Line 2 & 1.019 & 42.854 \\ Line 3 & 1.027 & 57.241 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: HVRT indicators considering the proposed key node as the control target. Figure 14: The generator terminal voltage variation curves, when taking the grid-connection node as the control target. (**a**) Line 1. (**b**) Line 2. (**c**) Line 3. Figure 15: The partial of generator terminal voltage variation curve, considering the grid-connection node as the control target. (**a**) Line 1. (**b**) Line 2. (**c**) Line 3. Figure 16: The generator terminal voltage variation curves, adopting the proposed strategy. (**a**) Line 1. (**b**) Line 2. (**c**) Line 3. Figure 17: The partial of generator terminal voltage variation curve, adopting the proposed strategy. (**a**) Line 1. (**b**) Line 2. (**c**) Line 3. Comparing the voltage generator terminal voltage variation curve of the wind turbines and the HVRT indicator data of the wind farms in the two cases, by adopting the proposed HVRT strategy in this article, the maximum generator terminal voltage of the wind turbines in the fault state is lower than 0.056 average VSI, and the ride-through time is shortened to about 33 ms average RTT.