Correction by pole placement
Principes généraux de correction

The adjustments described above are simple, and involve eliminating the dominant time constant of the process. They are therefore not applicable to unstable open-loop systems. These adjustments are a special case of a more general technique known as pole placement, which introduces into the corrector a sufficient number of parameters to arbitrarily shift the position of the roots of the characteristic equation in the complex plane. It is known (see...