Stabilization of unstable steady states in an electrochemical system using derivative control

We report the stabilization of an unstable fixed point in both an electrochemical experiment and a model for electrochemical corrosion using a small control signal proportional to the derivative of a measurable function of system variables. Spontaneous periodic oscillations observed during the potentio- static electrodissolution of a rotating copper disk in a sodium acetate–acetic acid buffer were suppressed to steady state behavior by adding to the anodic potential a feedback term proportional to the derivative of the electrical current passing through the cell. A general discussion of derivative control strategies shows that the steady state fixed points are left unchanged while, at the same time, the stability of the fixed points can be altered. We also show that, in general, the dimension of the state space of the system is increased when a derivative control strategy is applied.