Proportional Integral (PI) and Proportional Integral Derivative (PID) controllers have been at the heart of control engineering practice for seven decades. However, in spite of this, the PID controller has not received much attention from the academic research community until the past fifteen years, when work by K.J. Astrom, T. Hagglund and F.G. Shinskey, among others, has sparked a revival of interest in the use of this "workhorse" of controller implementation.
