\node[circle,draw=black,scale=0.6] (sum) at (1.5,0) {};
\node[anchor=east] at (-0.5,0) {$u_{\mathrm{i}}$};
\draw[-{Latex[round]},thick] (-0.5,0) -- (sum.west);
\node[anchor=south east, font=\footnotesize] at (sum.west) {+};

\draw[thick] (3,0.7) -- (4.5,0) -- (3,-0.7) -- cycle;
\node[] at (3.5,0) {$H_{\infty}T$};
\draw[-{Latex[round]},thick] (sum.east) -- (3,0);

\draw[thick] (4.5,-1.6) -- (3,-2.3) -- (4.5,-3) -- cycle;
\node[] at (4,-2.3) {$\frac{1}{H_{\infty}}$};
\draw[-{Latex[round]},thick] (3,-2.3) -- (1.5,-2.3) -- (sum.south);
\node[anchor=north west, font=\footnotesize] at (sum.south) {-};

\draw[thick] (3,1.6) -- (4.5,2.3) -- (3,3) -- cycle;
\node[] at (3.5,2.3) {$H_{\mathrm{0}}$};
\node[circle,draw=black,fill=black,scale=0.5] () at (0.25,0) {};
\draw[-{Latex[round]},thick] (0.25,0) -- (0.25,2.3) -- (3,2.3);
\node[circle,draw=black,scale=0.6] (sum2) at (6,0) {};
\draw[-{Latex[round]},thick] (4.5,0) -- (sum2.west);
\draw[-{Latex[round]},thick] (4.5,2.3) -- (6,2.3) -- (sum2.north);
\node[anchor=south east, font=\footnotesize] at (sum2.west) {+};
\node[anchor=south west, font=\footnotesize] at (sum2.north) {+};
\draw[-{Latex[round]},thick] (sum2.east) -- (8.5,0);
\node[circle,draw=black,fill=black,scale=0.5] at (7,0) {};
\draw[-{Latex[round]},thick] 
  (7,0) -- (7,-2.3) -- (7,-2.3) -- (4.5,-2.3);
\node[anchor=west] at (8.5,0) {$u_{\mathrm{o}}$};