Digital Closed Loop Control Technology for the AC Contactors

Abstract:
This paper presents a digital close loop control technology for AC contactors that include making close loop and keeping close loop using the digital power supply chip. As the current inner loop, the high-speed ADC samples the coil current actual value and compares with the coil current given value; therefore an error can be given to update the digital duty cycle. During the making process of the contactor, the motion electromotive force of the movable core compels the coil current falling. The falling slope directly relates to the velocity of the movable core, the sharper the slope, the higher the velocity. So the coil current falling slope can reflect the velocity of the movable core indirectly. As a velocity outer-loop, the measured value of the falling slope is compared with the given value of the slope and the error sets the coil current given value. Contact bounces and electrical wear can be reduced greatly by setting the proper given value of the slope. It improved the reliability and the electrical life of the AC contactors. The control scheme has good application prospect, particularly in the control of the largecapacity contactors.