# Load Frequency Control for Multi-Area Power Plants with Integrated Wind Resources
## 4 State Observer Based on Sliding Mode Control Strategies
### Simulation 2  
In other to test the proposed SOboSMC for the real MAIPS, a New England 39 bus power system (PS) was used. The configuration and parameters of the power system in this simulation were taken from [34].  
In addition, the importance of integrating renewable energy with MAIPSs has been discussed in [32]. Therefore, we considered integrating wind energy with area 1 at bus 5 and area 3 at bus 21 of the New England 39 bus PS. A single line diagram of the New England 39 bus PS integrated with a wind plant is shown in Figure 16. The proposed SOboSMC was tested for the LFC of the New England PS with and without wind plants. The wind variation was assumed as shown in Figure 17 and the load disturbance was applied for the MAIPS as shown in Figure 18. On the other hand, the SMC combined with the disturbance observer was used to increase the damping ratio for the LFC of the New England PS under random loads, as given in [34]. However, the stability of the frequency and tie-line power of the PS were attained without wind variation and the controller was required to measure all the system state variables. IN addition, an observer-based SMC used for the LFC of a New England PS was also seen in [32]. However, that controller suffered from chattering problems due to the first-order SMC used and the stability of the New England device was also achieved while neglecting wind disturbance. Therefore, there are doubts about the above approaches' applications in the LFC of a real PS integrated with renewable energies.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Kind of Controller** & \multicolumn{2}{c}{**Proposed SOboSMC**} & \multicolumn{2}{c}{**Double Integral SMC [23]**} \\ \hline Parameters & \(T_{s}(t)\) & _Max.O. S (pu)_ & \(T_{s}(t)\) & _Max.O. S (pu)_ \\ \(\Delta f_{1}\) & 3 & \(-5.8\times 10^{-3}\) & 7 & \(-0.06\) \\ \(\Delta f_{2}\) & 3 & \(-6.5\times 10^{-3}\) & 7 & \(-0.07\) \\ \(\Delta f_{3}\) & 3 & \(-11.5\times 10^{-3}\) & 7 & \(-0.07\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Setting time and maximum overshoot of the proposed state observer based on sliding mode control (SOboSMC) and double-integral SMC [23].  
Figure 15: Tie-line power deviation of three-area power system with a wind plant.  
Figure 16: Diagram of IEEE 39-bus integrated with wind plant.  
Figure 17: Wind speed variation.  
Therefore, the New England PS was simulated with and without wind plants to test the proposed continuous decentralized second-order SMC based observer. Figures 19 and 20 illustrate the results of the frequency error and the tie-line power error of the New England PS without wind. With the use of system states estimated by the observer, the frequency maximum overshoot and settling time were comparatively lower than the results presented in [34]. This is evidence that the new approach has a higher damping ratio than the scheme in [34]. In addition, the proposed approach solved the chattering phenomenon inherent in the first-order SMC presented in [32]. On the other hand, Figures 21 and 22 display the results of the frequency deviation and tie-power error of the New England PS with wind turbines. As seen in Figures 21 and  
**Remark 4**.: _An SMC based on the observer used for the LFC of the New England PS can be seen in [34]. However, there are two limitations of the above approach. The first is that the system state variables need to be measured in order to provide feedback for the controller. The second is that the  
Figure 21: Frequency deviation with wind plant.  
Figure 22: Tie-line power deviation with wind plant.  
Figure 20: Tie-line power deviation without wind plant.  
control suffers from the chattering problem inherent in the first-order SMC. In this approach, the state observer is used in the sliding surface and second-order sliding mode controller. Therefore, the two above limitations have been solved._