# Adjustable Capacity Evaluation Method Based on Step-by-Step Power Mapping of Offshore Wind Farms
## 4 Result
### Wind Farm Power Mapping  
Input the clustered power of the wind turbines into the first mapping to calculate the power of the collector system. The number of clusters is 12, and the number of hidden layer nodes of the neural network is set to 8. The results are shown in Figure 13.  
Comparing the errors calculated by the clustered power and the original power of the wind turbines, the errors are shown in Table 2.  
Figure 13: Calculation results of mapping from wind turbine clustered power to collector system power.  
It can be seen from the error comparison that the error of the collector system power calculating after the wind turbine power is spectrally clustered is smaller than that of using the original power.  
The calculated power of the collector system is input into the BP network to calculate the submarine cable loss, and the results are shown in Figure 14.  
The \(MAE\) is 0.18 MW and \(RMSE\) is 0.24 MW, which is almost the same as the error in the first part of the example analysis, indicating that the power fitting effect of the power collection system is ideal.  
After the calculation results of the collector system power and the cable loss of the submarine cable are obtained, the power of the collector system is subtracted from the loss of the offshore station, the loss of the submarine cable, and the loss of the onshore part at the corresponding time point, which is the final power of the grid connection point. The calculation results are shown in Figure 15.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Input** & \(MAE\) **(MW)** & \(RMSE\) **(MW)** \\ \hline Original power & 1.96 & 2.75 \\ Clustered power & 1.63 & 2.14 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Comparison of errors in the power calculation results of the collector system.  
Figure 14: Result of cable loss calculation.  
Figure 15: Step-by-step mapping of grid connection point power calculation results.  
In the practical application of offshore wind farms, the SCADA system of the wind turbine is independent of the monitoring systems of other parts, and only collects the relevant data of the wind turbines, and the wind farm AGC system uses the collected maximum theoretical power of the wind turbine to convert the wind farm's possible output. In order to verify the effectiveness of the method proposed in this paper, the two methods are compared:  
Method 1: In the segmented power mapping model proposed in this paper, the wind turbine power is input into the wind turbine power to collector system power mapping, and then the collector system power mapping result is input into the submarine cable loss calculation model. The power of the collector system after deducting various losses is the power at the grid connection point of the wind farm.  
Method 2: Direct power mapping model, which takes the power of each wind turbine as the input and the power of the wind farm grid connection point as the output, and calculates based on the BP network.  
The errors calculated by the two methods are compared in Table 3.  
By comparison, it can be seen that the step-by-step mapping method of wind farm power proposed in this paper can better reflect the real change trend than the direct calculation of wind turbine power. And the error is significantly reduced, which verifies the effectiveness and superiority of the proposed method.  
Compared with the direct mapping method, the loss in the power transmission process of the wind farm is considered more carefully. The calculation of the cable loss of the submarine cable is taken into account, and the power model of plant power and reactive power devices is realized. The characteristic modeling of the model effectively reduces the calculation error. Using the maximum theoretical generating power of wind turbines to calculate based on the method proposed in this paper, the adjustable capacity of offshore wind farms can be obtained, which provides a reference for grid dispatching.