Sensorless Online Opening Time Estimation of Contactors

Abstract

This paper proposed a sensorless online opening time estimation method of contactors based on the coil current. In the proposed method, the electromotive force containing the armature displacement information was converted into the coil current by controlling the coil voltage, and the opening time was estimated according to the corresponding relationship between the coil current peak and the armature displacement when contacts just part. The relationship was deduced theoretically from the mechanical armature motion and the variation of coil inductance. According to the relationship, a compensation resistor was configured in the coil activation circuit to improve estimating precision. Compared with the opening time estimation method based on contact voltage, the proposed method has higher estimating precision, which can keep the fracture of contacts and meet the requirements of miniaturization at the same time. The estimation results can be used as feedback to establish an application example: a zero point-on-wave opening whose delay can adjust automatically according to the change of opening time. The feasibility of the proposed estimation method is proved by an experiment in different contactors.