Input Power Factor Improvement Using Sensorless Single-Stage Axial Field PMDC Motor Controller for Arc Welding Process

Arc welding process involves high-intensity moving energy source in the form of electric arc. For creating joint, the heat source moves along the line of joint being created on the workpiece. Control of automatic (zero human assistance) or semi-automatic (manual movement of heat source) arc welding processes could require not only feeding of electrode material at constant rate but also the movement of electrode tip, often, more controlled motions. Due to superior control and actuation features the axial field pancake PMDC motors are more suitable. Due to their small value of armature time constant, when driven by PWM controller at moderate frequency, the armature current tends to be discontinuous. It allows the back-EMF be sampled for speed feedback and with proper power converter configuration and control the power factor could as well be improved. This article proposes a design of single-stage power controller for controlled and accurate movements of electrode tip sensorless and achieves multiple features such as improved power factor, reduced stress on components, reduced component count, high reliability, reduced current surge at start, longer life of magnets. It also details practical implementation of the idea and demonstrates the advantages claimed.