Addition of disturbance to microgrid system

I have a microgrid system which is represented in state space model by x dot = Ax . The dimension of A is 32*32. I want to introduce a step disturbance in one of the states and plot the resulting response of some states in MATLAB/SIMULINK. How will I get the response of some states with time as the step input disturbance in one of the state is introduced ? What should be my B,C and D matrix