# Enhanced Quasi Type-1 PLL-Based Multi-Functional Control of Single-Phase Dynamic Voltage Restorer
## 5 Simulation and Experimental Results  
In this Section, simulation and experimental results are reported. The experimental setup used in this study is demonstrated in Figure 8. Here, a Texas Instrument C2000 series micro-controller is used to implement the proposed control and estimation algorithm. Parameters of the setup and control gains are provided in Table 1.  
Figure 8: Experimental setup used in this study. Numerical simulation using Matlab/Simulink is conducted by considering the same values. In the first test, the grid voltage suddenly experiences a \(\approx\)30% sag. From approximately 170 V (peak), the grid voltage dropped to roughly 120 V (peak). Experimental results are provided in Figure 9. The results show that in order to mitigate the effect of grid voltage sag at the sensitive load side, the DVR was very quick to react and supplied the necessary 50 V in-phase compensation voltage. As a result, constant voltage was maintained at the load side. In the second test, voltage swell was considered, and the results are provided in Figure 10. Here, grid voltage increased to 210 V, which is roughly a 25% change from the nominal value. Unlike the first test, here, out-of-phase compensation voltage needs to be generated in order to reduce the voltage at the sensitive load end. As shown in Figure 10, the proposed enhanced QT1-PLL was very successful in generating the required roughly 40 V out-of-phase compensation voltage, and the sliding mode controller ensured the tracking of the reference compensation voltage by the DVR. These results show that the proposed approach can handle both sag and swell conditions. In the real grid, in addition to voltage sag/swell, harmonics are also a problem. The presence of harmonics will render the sensitive load voltage distorted. As a result, power quality degrades. In order to mitigate this issue, harmonic compensation is also required. In the final test, the grid voltage suddenly became distorted, and the results are provided in Figure 11. The proposed PLL can extract the fundamental component with high harmonic robustness. As a result, quick estimation of the grid harmonics was performed by PLL, and DVR injected the necessary harmonic compensation voltage to ensure very low distortion at the load side. The results in Figure 11 validate the suitability of the proposed PLL in a distorted grid condition. \begin{table}
\begin{tabular}{c c} \hline \hline
**System and Control Parameters** & **Values** \\ \hline Controller gains & \\ PLL gain & \(k_{f}=89\) \\ Grid: voltage and frequency & 120 V (rms) 50 Hz \\ Grid: impedance & \(R_{g}=1\) m\(\Omega\), \(L_{g}=0.1\) uH \\ Transformer turns ratio & 1:1 \\ DC link voltage, \(V_{dc}\) & 120 V \\ LC filter & \(L_{f}=0.8\) mH, \(C_{f}=50\) μF \\ Sensitive series load & \(R=100\)\(\Omega\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Experimental study parameters. Figure 9: Experimental responses of \(v_{g},v_{c}\), and \(v_{L}\) subject to voltage sag in the grid. In order to check the robustness of the used controller, we have used numerical simulations. In the simulation test, voltage sag and harmonics are considered. The nominal value of the filter inductor is 0.8 mH. This value is used to synthesize the control law. Simulation results with \(\pm 25\%\) variation in the filter inductor are provided in Figure 12. The results in Figure 12 show that the response of DVR is very similar when the system parameter experienced a \(\pm 25\%\) change from the nominal value. This shows that the sliding mode controller is robust to parameter variations. Experimental results as shown in Figures 9-11 independently considered voltage sag, swell, and harmonics. In practice, in addition to these characteristics, phase and/or frequency of the grid voltage may also change simultaneously in the worst case scenario. In order to asses the performance of the proposed method, two additional simulation studies were considered. In the first test, grid voltage experienced \(-0.5\) p.u. sag and \(-25^{\circ}\) phase change simultaneously.