\begin{tikzpicture}[>=latex]
\matrix[]
{
      \pgftransformscale{.7}
      \fill[gray!30] (0,0) -- (0,0.5625) -- (0.45,0);
      \fill[gray!30] (4,0) -- (2.325,0) -- (3,0.5625) -- (4.0,0.5625);
      \fill[gray!60] (0.45,0) -- (1.2,-0.9375) -- (2.325,0);
      \draw (0,0.5625) -- (0,0.5625) -- (1.2,-0.9375) -- (3,0.5625) -- (4,0.5625);
      % horizontal axis
      \draw[->] (-0.2,0) -- (0.5+4,0) node[right] {$t$};
      \draw (1.2,0) -- (1.2,0.1) node[above] {$T_1$};
      \draw (3.0,0) -- (3.0,-0.1) node[below] {$T_2$};
      \draw (4.0,0) -- (4.0,-0.1) node[below] {$T_s$};
      % vertical axis
      \draw[->] (0,-1.7) -- (0,1.0) node[above] {$i_{C_{in}}(t)$};
      \draw (0,0.5625) -- (-0.1,0.5625) node[left] {$I_{in}$};
      \draw (0,-0.9375) -- (-0.1,-0.9375) node[left] {$i_2$};
      \draw (2.5,1.8) node { \textbf{a} };
      \draw (2.5,1.3) node { \scriptsize $k_B = 1$ };
&
      \pgftransformscale{.7}
      \fill[gray!30] (0,0) -- (0,0.225) -- (0.18,0);
      \fill[gray!30] (4,0) -- (1.2,0) -- (1.2,0.225) -- (4.0,0.225);
      \fill[gray!60] (0.18,0) -- (1.2,-1.275) -- (1.2,0);
      \draw (0,0.225) -- (1.2,-1.275) -- (1.2,0.225) -- (4,0.225);
      %
      \node (UT) at (2.0,-1.0) {\small $q_{ut}$};
      \draw[thin] (0.95,-0.6) -- (UT);
      \fill (0.95,-0.6) circle[radius=0.7mm];
      % horizontal axis
      \draw[->] (-0.2,0) -- (0.5+4,0) node[right] {$t$};
      \draw (1.2,0.225) -- (1.2,0.225) node[above] {$T_1$};
      \draw (3.0,0) -- (3.0,-0.1) node[below] {$T_2$};
      \draw (4.0,0) -- (4.0,-0.1) node[below] {$T_s$};
      % vertical axis
      \draw[->] (0,-1.7) -- (0,1.0) node[above] {$i_{C_{in}}(t)$};
      \draw (0,0.225) -- (-0.1,0.225) node[left] {$I_{in}$};
      \draw (0,-1.275) -- (-0.1,-1.275) node[left] {$i_2$};
      \draw (2.5,1.8) node { \textbf{b} };
      \draw (2.5,1.3) node { \scriptsize $k_B = 0$ };
&
      \pgftransformscale{.7}
      \fill[gray!30] (0,0) -- (0,0.225) -- (0.18,0);
      \fill[gray!30] (4,0) -- (1.2,0) -- (1.2,0.225) -- (4.0,0.225);
      \fill[gray!60] (0.18,0) -- (1.2,-1.275) -- (1.2,0);
      \draw (0,0.225) -- (1.2,-1.275) -- (1.2,0.225) -- (4,0.225);
      % horizontal axis
      \draw[->] (-0.2,0) -- (0.5+4,0) node[right] {$t$};
      \draw (1.2,0.225) -- (1.2,0.225) node[above] {$T_1$};
      \draw (3.0,0) -- (3.0,-0.1) node[below] {$T_2$};
      \draw (4.0,0) -- (4.0,-0.1) node[below] {$T_s$};
      % vertical axis
      \draw[->] (0,-1.7) -- (0,1.0) node[above] {$i_{C_{in}}(t)$};
      \draw (0,0.225) -- (-0.1,0.225) node[left] {$I_{in}$};
      \draw (0,-1.275) -- (-0.1,-1.275) node[left] {$i_2$};
      \draw (2.5,1.8) node { \textbf{c} };
      \draw (2.5,1.3) node { \scriptsize $k_B = 0$ };
\\[0.5ex]
\node at (1.5,0.4) {$i_1 = I_{in} - \min i_L$};
\node at (1.5,0.0) {$i_2 = I_{in} - \max i_L$};
&
\node at (1.5,0.4) {$q_{in}$ är ytan av de ljusgråa ytorna};
\node at (1.5,0.0) {$q_{ut}$ är ytan av de mörkgråa ytorna};
&
\node at (1.5,0.4) {$i_3 = k_t \min i_L - I_{ut}$};
\node at (1.5,0.0) {$i_4 = k_t \max i_L - I_{ut}$};
\\
      \pgftransformscale{.7}
      \fill[gray!30] (0,0) -- (0,-0.3375) -- (1.2,-0.3375) -- (1.2,0);
      \fill[gray!30] (4,0) -- (4.0,-0.3375) -- (3,-0.3375) -- (2.595,0);
      \fill[gray!60] (1.2,0) -- (1.2,1.1625) -- (2.595,0);
      \draw (0,-0.3375) -- (1.2,-0.3375) -- (1.2,1.1625) -- (3,-0.3375) -- (4,-0.3375);
      % horizontal axis
      \draw[->] (-0.2,0) -- (0.5+4,0) node[right] {$t$};
      \draw (1.2,-0.3375) -- (1.2,-0.3375) node[below] {$T_1$};
      \draw (3.0,0) -- (3.0,0.1) node[above] {$T_2$};
      \draw (4.0,0) -- (4.0,0.1) node[above] {$T_s$};
      % vertical axis
      \draw[->] (0,-1.5) -- (0,2.0) node[above] {$i_{C_{ut}}(t)$};
      \draw (0,1.1625) -- (-0.1,1.1625) node[left] {$i_4$};
      \draw (0,-0.3375) -- (-0.1,-0.3375) node[left] {$-I_{ut}$};
      \node at (2.0,-1.5) {K1};
      \draw (2.5,1.8) node { \textbf{d} };
      \draw (2.5,1.3) node { \scriptsize $k_A = 0$ };
&
      \pgftransformscale{.7}
      \fill[gray!30] (0,0) -- (0,-0.5625) -- (0.45,0);
      \fill[gray!30] (4,0) -- (2.325,0) -- (3,-0.5625) -- (4.0,-0.5625);
      \fill[gray!60] (0.45,0) -- (1.2,0.9375) -- (2.325,0);
      \draw (0,-0.5625) -- (1.2,0.9375) -- (3,-0.5625) -- (4,-0.5625);
      % horizontal axis
      \draw[->] (-0.2,0) -- (0.5+4,0) node[right] {$t$};
      \draw (1.2,0) -- (1.2,-0.1) node[below] {$T_1$};
      \draw (3.0,0) -- (3.0,0.1) node[above] {$T_2$};
      \draw (4.0,0) -- (4.0,0.1) node[above] {$T_s$};
      % vertical axis
      \draw[->] (0,-1.5) -- (0,2.0) node[above] {$i_{C_{ut}}(t)$};
      \draw (0,0.9375) -- (-0.1,0.9375) node[left] {$i_4$};
      \draw (0,-0.5625) -- (-0.1,-0.5625) node[left] {$-I_{ut}$};
      \node at (2.0,-1.5) {K2};
      \draw (2.5,1.8) node { \textbf{e} };
      \draw (2.5,1.3) node { \scriptsize $k_A = 1$ };
&
      \pgftransformscale{.7}
      \fill[gray!30] (0,0) -- (0,0.3375) -- (1.2,0.3375) -- (1.2,0);
      \fill[gray!30] (4,0) -- (4.0,0.3375) -- (3,0.3375) -- (2.595,0);
      \fill[gray!60] (1.2,0) -- (1.2,-1.1625) -- (2.595,0);
      \draw (0,0.3375) -- (1.2,0.3375) -- (1.2,-1.1625) -- (3,0.3375) -- (4,0.3375);
      % horizontal axis
      \draw[->] (-0.2,0) -- (0.5+4,0) node[right] {$t$};
      \draw (1.2,0.3375) -- (1.2,0.3375) node[above] {$T_1$};
      \draw (3.0,0) -- (3.0,-0.1) node[below] {$T_2$};
      \draw (4.0,0) -- (4.0,-0.1) node[below] {$T_s$};
      % vertical axis
      \draw[->] (0,-1.5) -- (0,2.0) node[above] {$i_{C_{ut}}(t)$};
      \draw (0,-1.1625) -- (-0.1,-1.1625) node[left] {$i_4$};
      \draw (0,0.3375) -- (-0.1,0.3375) node[left] {$-I_{ut}$};
      \node at (2.0,-1.5) {K3};
      \draw (2.5,1.8) node { \textbf{f} };
      \draw (2.5,1.3) node { \scriptsize $k_A = 0$ };
\\
};
\end{tikzpicture}
