\documentclass{article}
\usepackage{verbatim,tikz,longtable,booktabs,enumitem}
\usepackage{amsmath,amsfonts,amssymb}
\usepackage[american]{circuitikz}
\usetikzlibrary{calc,fit}
\usepackage{pgfplots}
\usetikzlibrary{arrows.meta}

\begin{document}
	
\begin{figure}[h!]
	\centering
	\tikzstyle{block} = [draw, fill=white, rectangle, 
	minimum height=3em, minimum width=6em, very thick]
	\tikzstyle{sum} = [draw, fill=white, circle, node distance=1cm, very thick]
	\tikzstyle{input} = [coordinate]
	\tikzstyle{output} = [coordinate]
	{\boldmath
		\begin{tikzpicture}[auto, node distance=2cm,>=latex,very thick]
		
		\node [input, name=input] {};
		
		\node [block, right of=input,node distance=2cm] (kp) {$ K_p$};
		\node [ left of=kp ,node distance=4cm] (kp1) ;
		\node [ right of=kp ,node distance=4cm] (kpp) ;
		
		\node [block, below of=kp,node distance=2cm] (ki) {$ K_i \int$};
		\node [left of=ki,node distance=4cm] (ki1);	
		\node [right of=ki,node distance=4cm] (kii);
		
		\node [block, below of=ki,node distance=2cm] (kd) {$ \dfrac{1}{K_d}\dfrac{d}{dt}$};
		\node [left of=kd,node distance=4cm] (kd1);
		\node [right of=kd,node distance=4cm] (kdd);
		
		\node [sum1, left of=ki ,node distance=4cm] (sum1) {};
		\node [sum, right of=ki ,node distance=4cm] (sum) {$+$};
		\node [end, right of=sum ,node distance=1.5cm] (end) {$u(t)$};
		\node [left of=ki1,node distance=1cm] (start){$ e_i$};	
		
		\draw [-] (start) -- (ki1);
		\draw [-] (sum1) -- (kp1);
		\draw [->] (kp1) -- (kp);
		\draw [-] (kp) -- (kpp);
		\draw [->] (kpp) -- (sum);
		
		\draw [->] (ki1) -- (ki);
		\draw [->] (ki) -- (kii);
		
		\draw [-] (sum1) -- (kd1);
		\draw [->] (kd1) -- (kd);
		\draw [-] (kd) -- (kdd);
		\draw [->] (kdd) -- (sum);
		
		\draw [->] (sum) -- (end);
		
		\node [output, right of=ki1, node distance=4cm] (output) {};
		\node [summ, left of=sum1] (summ) {};
		
		(sum);    	   
		\end{tikzpicture}}
	\caption{simple block}	
	\label{fig1}
\end{figure}


\end{document}