How do I correctly align this equation?
I'm not sure there's anything to align, except for the two big braces. Don't force alignment to objects that aren't related to one another.
\documentclass{article}
\usepackage{amsmath,bm}
\newcommand{\cchi}{\mathord{\mathop{\bm{\chi}}}}
\begin{document}
\begin{align}
\max\eta_D(\mathbf{J}_{\cchi_{k,l}}) &\in (0,1]
\\
\text{subject to }
&\left\{\begin{aligned}
&\alpha_{12}^j \le \dfrac{\pi}{6}\\
&\alpha_{23}^j \le \dfrac{\pi}{6}\\
&\!\max_{\cchi\in\Omega}|\beta_1^j| \le \dfrac{\pi}{12} \\
&\!\max_{\cchi\in\Omega}|\beta_2^j| \le \dfrac{\pi}{12} \\
&\!\max_{\cchi\in\Omega}|\beta_3^j| \le \dfrac{\pi}{12} \\
&\!\min_{\cchi\in\Omega}(\mathcal{D}_{\omega^j}) >0
\end{aligned} \right.
\\
\text{bounded by }
&\left\{\begin{aligned}
&{-}\dfrac{1}{12}\pi \le \varphi_1 \le \dfrac{1}{12}\pi\\
&{-}\dfrac{1}{12}\pi \le \varphi_2 \le \dfrac{1}{12}\pi\\
&0 \le \Theta_1 \le \dfrac{8}{45}\pi\\
&0 \le \Theta_2 \le \dfrac{8}{45}\pi\\
&0 \le \Theta_3 \le \dfrac{23}{180}\pi\\
&(\varphi_1^j, \Theta_1^j) \ne (\varphi_2^j,\Theta_2^j) \ne (0,\Theta_3^j)\\
&\varphi_2^j \ne 0
\end{aligned}\right.
\end{align}
\end{document}
With dcases
and nccmath
for medium size fractions:
\documentclass{article}
\usepackage{nccmath, mathtools}
\usepackage{bm}
\DeclarePairedDelimiter\abs{\lvert}{\rvert}
\newcommand{\bchi}{\mathord{\mathop{\bm{\chi}}}}
\begin{document}
\begin{align}
\max{\eta_D\left(\mathbf{J}_{\bchi_{k,l}}\right)}
& \in (0,1] \\
\text{subject to}
& \begin{dcases}
\alpha_{12}^j \le \mfrac{\pi}{6} \\
\alpha_{23}^j \le \mfrac{\pi}{6} \\
\max_{\bchi\in\Omega}\abs{\beta_1^j} \le \mfrac{\pi}{12} \\
\max_{\bchi\in\Omega}{\abs{\beta_2^j}} \le \mfrac{\pi}{12} \\
\max_{\bchi\in\Omega}{\abs{\beta_3^j}} \le \mfrac{\pi}{12} \\
\min_{\bchi\in\Omega}\bigl(\mathcal{D}_{\omega^j}\bigr) >0 \\
\end{dcases}\\
\text{bounded by}
& \begin{dcases}
-\mfrac{1}{12}\pi \le \varphi_1 \le \mfrac{1}{12}\pi\\
-\mfrac{1}{12}\pi \le \varphi_2 \le \mfrac{1}{12}\pi\\
0 \le \Theta_1 \le \mfrac{8}{45}\pi \\
0 \le \Theta_2 \le \mfrac{8}{45}\pi \\
0 \le \Theta_3 \le \mfrac{23}{180}\pi \\
(\varphi_1^j,\Theta_1^j) \ne (\varphi_2^j,\Theta_2^j) \ne (0,\Theta_3^j)\\
\varphi_2^j \ne 0
\end{dcases}
\end{align}
\end{document}