Input Power Factor Improvement Using Sensorless Single-Stage Axial Field PMDC Motor Controller for Arc Welding Process
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ORIGINAL CONTRIBUTION
Input Power Factor Improvement Using Sensorless Single-Stage Axial Field PMDC Motor Controller for Arc Welding Process Arun Kumar Paul1
Received: 12 September 2019 / Accepted: 13 August 2020 Ó The Institution of Engineers (India) 2020
Abstract 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 singlestage 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. Keywords Back electromotive force (back-EMF) Inherent power factor improvement Permanent magnet direct current (PMDC) motor P/PI switchable control function
& Arun Kumar Paul [email protected] 1
R & D Department, Electronics Devices World Wide Private Limited, 22 Mistry Industrial Estate, Cross Road A, MIDC, Andheri (East), Mumbai, Maharastra 400093, India
Reduced de-magnetizing current Single-stage multi-feature sensorless speed control
Introduction Though the application prospect of brushed DC motors is on decline, they are still preferred in several low power applications. Axial field PMDC motors [1–3], in particular, are used for controlled movements of objects in several process applications, such as, of electrode tip in various arc welding processes [4–7]. For accurate speed control, often, the back-EMF of PMDC motor is used [3] as feedback. In arc welding process, in particular, the sensorless speed control option is beneficial because it simplifies the configuration of controller, reduces electrical interconnections and controller’s overall cost is also significantly reduced. To enable back-EMF sensing, the PWM controller is so driven that the motor current is discontinuous [2]. The scope of motor control in arc welding is huge. Several processes such as cold metal transfer [7] need fast acting motor controller [3], whereas traditional gas metal arc welding (GMAW) process, for a particular welding condition, requires constant speed [5] of electrode tip as well as constant fe
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