## 4 Results and Discussions
### Experimental Results
#### 4.2.2 Unbalanced and Distorted Grid  
Grid distortion is often inevitable. So, this test considers unbalance and distortion at the same time. In this test, initially balanced grid is consider with 1.0 p.u. positive sequence component. After the fault, negative sequence of 0.1 p.u. and zero sequence of 0.05 p.u. are added. In addition, 5 th and 13 th-order positive sequence harmonics of 0.015 p.u. and 0.012 p.u. and 7 th-order negative sequence harmonics of 0.017 p.u. are added. So, the negative sequence component has a distortion of 17% which is a highly challenging test scenario. Experimental results are given in Figure 7. Due to the presence of distortion in the voltage, the estimated frequencies also have estimation ripple. Similar to the previous test, GAO has the highest peak overshoot (\(\approx\)0.5 Hz) and steady-state estimation ripple (\(\approx\)0.3 Hz). SAO demonstrated the lowest peak overshoot (\(\approx\)0.3 Hz) and steady-state estimation ripple (\(\approx\)0.1 Hz). Based on simulation and experimental results, a comparative summary of the adaptive observer-based techniques are presented in Table 1. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Characteristics** & **GAO** & **GNAO** & **SAO** \\ \hline Dynamic Performance & Very Fast & Very Fast & Very Fast \\ \hline Voltage Sag Sensitivity & High & Low & Low \\ \hline Harmonic Disturbance & Good & Very Good & Very Good \\ \hline DC Offset Rejection & Good & Very Good & Very Good \\ \hline Computational Complexity & Medium & High & Medium \\ \hline \hline \end{tabular}
\end{table} 
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