Please, help with this, I didn't know how to solve it. Here's the code:
\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[big,online]{dgruyter}
\usepackage{lmodern}
\usepackage{microtype}
\usepackage{amsfonts,amssymb,amsmath,amsgen,amsopn,amsbsy,theorem,graphicx,epsfig}
\usepackage[numbers,square,sort&compress]{natbib}
\usepackage{subcaption}
\usepackage{caption}
\begin{document}
\begin{table}[!hbt]
\tiny
\begin{center}
\begin{minipage}{\textwidth}
\caption{Overshoots and undershoots of $\delta_\text{sym}, \omega_\text{syn}, P_\text{dfig}, I_\text{dr}, I_\text{qr}, I_\text{statcom}$ for all cases.\strut}
$\begin{tabular}{cccccccccc}
%\toprule
&\multicolumn{3}{c}{Case 1 (No PSS/No STATCOM)} & \multicolumn{3}{c}{Case 2 (Only PSS)} & \multicolumn{3}{c}{Case 3 (PSS + STATCOM)}\\
\cmidrule(lr){2-4}\cmidrule(lr){5-7}\cmidrule(lr){8-10}
& 0.2 pu & 0.4 pu & 0.6 pu & 0.2 pu & 0.4 pu & 0.6 pu & 0.2 pu & 0.4 pu & 0.6 pu \\
\midrule
\multirow{2}{*}{$\delta_1$ (pu)} &{+1446\%} & \multirow{2}{*}{{Instable}} & \multirow{2}{*}{{Instable}} &{+1616\%} &{+2300\%} &{+5126\%} &{+1000\%} &{+1396\%} &{+3130\%} \\
&{-2676\%} & & &{-1491\%} &{-2110\%} &{-4794\%} &{-438\%} &{-1474\%} &{-2937\%} \\
%\midrule
\multirow{2}{*}{$\delta_2$ (pu)} &{+70\%} & \multirow{2}{*}{{Instable}} & \multirow{2}{*}{{Instable}} &{+70\%} &{+63\%} &{+55.3\%} &{+31\%} &{+46\%} &{+40.26\%} \\
&{-117\%} & & &{-63\%} &{-54\%} &{-51.6\%} &{-17\%} &{-39\%} &{-31.46\%} \\
%\midrule
\multirow{2}{*}{$\delta_3$ (pu)} &{+61\%} & \multirow{2}{*}{{Instable}} & \multirow{2}{*}{{Instable}} &{+78\%} &{+68\%} &{+59.2\%} &{+29\%} &{+51\%} & {+43.6\%} \\
&{-121\%} & & &{-66\%} &{-49\%} &{-41.3\%} &d{-10\%} &{-36\%} &{-27\%} \\
%\midrule
\multirow{2}{*}{$\omega_1$ (pu)} &{+0.4\%} & \multirow{2}{*}{{Instable}} & \multirow{2}{*}{{Instable}} &{+0.3\%} &{+0.3\%} &{+0.3\%} &{+0.3\%} &{+0.3\%} & {+0.3\%} \\
&{-0.34\%} & & &{-0.23\%} &{-0.21\%} &{-0.22\%} &{-0.21\%} &{-0.21\%} &{-0.21\%} \\
%\midrule
\multirow{2}{*}{$\omega_2$ (pu)} &{+0.6\%} & \multirow{2}{*}{{Instable}} & \multirow{2}{*}{{Instable}} &{+0.5\%} &{+0.5\%} &{+0.5\%} &{+0.5\%} &{+0.5\%} &{+0.5\%} \\
&{-0.54\%} & & &{-0.34\%} &{-0.37\%} &{-0.39\%} &{-0.33\%} &{-0.37\%} &{-0.41\%} \\
%\midrule
\multirow{2}{*}{$\omega_3$ (pu)} &{+0.7\%} & \multirow{2}{*}{{Instable}} & \multirow{2}{*}{{Instable}} &{+0.7\%} &{+0.7\%} &{+0.7\%} &{+0.7\%} &{+0.7\%} &{+0.7\%} \\
&{-0.54\%} & & &{-0.32\%} &{-0.3\%} &{-0.31\%} &{-0.31\%} &{-0.3\%} &{-0.34\%} \\
%\midrule
\multirow{2}{*}{$P_\text{dfig}$ (pu)} &{+22\%} & \multirow{2}{*}{{Instable}} & \multirow{2}{*}{{Instable}} &{+27.4\%} &{+12.7\%} &{+7.9\%} &{+13.5\%} &{+6.5\%} &{+4.2\%} \\
&{-16.4\%} & & &{-15.1\%} &{-5.6\%} &{-3.66\%} &{-4\%} &{-4.4\%} &{-2.75\%} \\
%\midrule
\multirow{2}{*}{$I_\text{dr}$ (pu)} &{+17\%} & \multirow{2}{*}{{Instable}} & \multirow{2}{*}{{Instable}} &{+9.7\%} &{+7.9\%} &{+5\%} &{+23\%} &{+19.8\%} &{+17\%} \\
& {$I_{\text{dr}_\text{min}}$} & & & {$I_{\text{dr}_\text{min}}$} &{$I_{\text{dr}_\text{min}}$} &{$I_{\text{dr}_\text{min}}$} & {$I_{\text{dr}_\text{min}}$} & {$I_{\text{dr}_\text{min}}$} & {$I_{\text{dr}_\text{min}}$} \\
%\midrule
\multirow{2}{*}{$I_\text{qr}$ (pu)} &{+56\%} & \multirow{2}{*}{{Instable}} & \multirow{2}{*}{{Instable}} &{+56.5\%} &{+19.3\%} &{+8.5\%} &{+60\%} &{+23\%} &{+12.46\%} \\ &{$I_{\text{qr}_\text{min}}$} & & & {$I_{\text{qr}_\text{min}}$} &{$I_{\text{qr}_\text{min}}$}&{$I_{\text{qr}_\text{min}}$} & {$I_{\text{qr}_\text{min}}$} & {$I_{\text{qr}_\text{min}}$} & {$I_{\text{qr}_\text{min}}$} \\
$I_\text{statc}$ (pu) &--- &--- &--- &--- &--- &--- &{+598\%} &{+748\%} &{+717\%} \\
\noalign
\label{tab1:Table1}
\end{tabular}$
\end{minipage}
\end{center} %vs{-4mm}
\end{table}
\end{document}
here are also the sytle files https://file.fm/u/gd4cvpeez Thanks in advance
\labelfor the table, but no\caption. Unrelated: your preamble forgets to loadmultirowandbooktabs.amsfontsif you loadamssymb. Similarly,amsopn, amsbsydon't have to be loaded when you loadamsmath.\delta_\text{sym}like this. (1) it does not do what you think (which I'm assuming writing upright text) and (2) it is rather dangerous to assume that_\text{foo}will always work, the promoted solution is always to use_{...}. Here I'd just use_{\textup{sym}}instead. (Sadly this misuse of the\textcommand is very common)