Advanced Control of a Resistance Spot Welding System

• Published in: IEEE transactions on power electronics Vol. 23; no. 1; pp. 144 - 152
• Main Authors: Klopcic, Beno, Dolinar, Drago, Stumberger, Gorazd
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.01.2008; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Circuit faults; Circuit properties; Circuits; Control systems; Convertors; Current control; dc-dc converters; Diodes; Electric currents; Electric resistance; Electric, optical and optoelectronic circuits; Electrical engineering. Electrical power engineering; Electrical machines; Electronic circuits; Electronic equipment and fabrication. Passive components, printed wiring boards, connectics; Electronics; Exact sciences and technology; high-frequency transformers; Iron; Ohmic; Pulse transformers; Pulse width modulation converters; Rectifiers; Resistance spot welding; saturable cores; Signal convertors; Spot welding; Transformer cores; Transformers; Transformers and inductors; Voltage control; Welding; Welding current; Closed loop; Rectifier; Voltage transformer; Rise time; Diode; Control system; Secondary circuit; Direct current convertor; Resistance spot welding; Transformer cores; Magnetic saturation; DC-DC power convertors; saturable cores; Current control; Hysteresis loop; dc-dc converters; Selector switch; High-frequency transformers; Pulse duration modulation; Resistor; Overcurrent protection
• ISSN: 0885-8993; 1941-0107
• DOI: 10.1109/TPEL.2007.911851

This paper deals with a middle-frequency resistance spot welding system. It consists of an input converter, welding transformer, and a full-wave rectifier mounted at the transformer secondary. The welding current at the full-wave rectifier output is normally controlled by the pulse width modulated primary voltage of the transformer supplied by the input converter. The unequal ohmic resistances of the two transformer's secondary circuits and the different characteristics of the diodes of output rectifier certainly lead to the magnetic saturation which, consequently, causes the unwanted spikes in the transformer's primary current and over-current protection switch-off. This disadvantage of classical spot welding systems is completely eliminated by the proposed advanced hysteresis controller (AHC), which keeps transformer iron core saturation within prescribed bounds regardless of how unequal the ohmic resistances and diodes' characteristics in the transformer's secondary circuits are. This is achieved by a combined closed-loop control of the welding current and closed-loop control of the iron core saturation level. The proposed AHC assures a very short rise time of the welding current and the best possible utilization of the transformer iron core.