PID Controllers, Part IV: Proportional control can make a system unstable, 28/11/2013
Channel: Lutfi Al-Sharif
Date: 2013-11-29

This video shows, through the use of a Simulink file, how a proportional controller can make a third order system unstable.  It uses trial and error to find the value of K that makes the system unstable.  The third order system is shown as a series of first order systems (time lags).  At lower values of K the closed loop system is stable, but the setting of the value of K is a compromise between the overshoot and rise time and between the steady state error.  The example is ideal for showing the limitations of a proportional controller.