Sensorless Control and Fault Diagnosis of Electromechanical Contactors

This paper describes a novel algorithm for a closed-loop sensorless control of electromagnetic devices. It integrates a novel fault diagnosis algorithm of the whole electromagnetic circuit. Applied to a contactor with a dc core, it eliminates the armature and contact bounce, whether it is ac or dc powered and at either 50 or 60 Hz. The position and velocity of the moving armature and contacts are calculated by means of the online determination of the inductance using only the measured current and voltage values of the contactor coil as control inputs. A fuzzy controller takes the position and velocity of the armature as input and provides the current set point as output, which controls the velocity of closure of the contacts. The algorithm has been implemented in a low-cost electronic module.