Mid Sweden University

A technique for measuring the current of a stationaryspot welding unit using a Hall sensor system is implemented. HallEffect sensor is used to sense the strength of the magnetic fieldproduced by the current, flowing through the welding electrodes,on the secondary side of welding transformer. In contrast to acurrent transformer the Hall Effect sensor can read a DC currentand can thus be utilized in direct current welding equipments. Inthis paper the influence of the sensor position and presence of thetools or other materials in the proximity of the sensor that effectthe sensor reading is investigated. COMSOL Multiphysicssoftware is used to investigate these effects and a circuit design isimplemented according to the conclusion drawn from the simulations.

Inverter drive resistance spot welding machines are becoming a good choice of welding because of the increased machine efficiency and output power. The DC link capacitors in spot welding equipment store a large amount of energy. In case of any failure, the IGBT in the inverter has a risk of exhibiting a violent rupture. This rupture can damage the converter, drive down time and personal injury which may lead to the machinery certification problems. IGBT failure detection and solution for protection of these failures in resistance welding machines have not been reported in literature. Literature study of the IGBT failure, rupture, fault detection and protection has been carried out for inverter drives in power applications. On the basis of the findings some protection schemes and important measures in the design of the machine have been adopted which have resulted in the reduced risk of IGBT failure.

In designing switch mode power supply (SMPS), thedesirable feature is to have an efficient and compact design. Themain idea is to increase the switching frequency and reduce thebulky magnetic parts of the converter. This leads to a compactsize, less weight, reduced cost and increased power density of theconverter. This paper presents a high frequency full bridge DC toDC converter, using a multilayer coreless printed circuit board(PCB) step-up power transformer. The converter was simulatedand also implemented on the PCB. The pulse width modulated(PWM) signals were generated, using a microcontroller, to switchthe Metal oxide semiconductor field effect transistor (MOSFET).The design of the converter is tested up to the power levels of 5Watts with the switching frequency in 2 to 3MHz range. Theenergy efficiency of the converter is 74.86% at 2.4 MHz.

Resistance spot welding process comprises of electric, thermal and mechanical phenomenon, which makes this process complex and highly non-linear and thus, it becomes difficult to model it. In order to obtain good weld nugget during spot welding, hit and trial welds are usually done which is very costly. Therefore the numerical simulation research has been conducted to understand the whole process. In this paper three different cases were analyzed by varying the tip contact area and it was observed that, with the variation of tip contact area the nugget formation at the faying surface is affected. The tip contact area of the welding electrode becomes large with long welding cycles. Therefore in order to maintain consistency of nugget formation during the welding process, the current compensation in control feedback is required. If the contact area of the welding electrode tip is reduced, a large amount of current flows through the faying surface, as a result of which sputtering occurs.

With the emerging power semiconductor devices in GaN and SiC technology and the development of high frequency multilayered PCB power transformers, power efficient DC-DC converters are designed in megahertz switching frequency range. The increased switching frequency in combination with sudden changes in current “di/dt” or voltage “dv/dt” levels generate higher order harmonics, which cause Electro Magnetic Interference (EMI). One of the major challenges, to design the power stage of these converters, is to minimize the EMI because it affects their Electro Magnetic Compatibility (EMC). There is a spread belief that the EMI becomes much worse in a MHz switching converter compared to the current ones operating below 150 kHz. This paper investigates the consequences on implementation of a line filter for suppressing conducted EMI in high frequency power converters. The results are based on electronic simulations, comparing EMI and filter design, for a 200 kHz and 2 MHz buck converter under similar conditions. By analyzing the noise frequency spectrum of both the converters it is observed that the size of filter components, such as capacitors and common mode chokes is greatly reduced in case of 2MHz Buck converter. The results show that the size reduction that can be accomplished by increasing the switching frequency to MHz range can be improved further by a smaller implementation of the line filter as well.

The versatility, rich mathematical formulations and robustness of finite element methods make them attractive for simulations for a wide range of problems. Two dimensional models concerning the seam welding process do have some limitations. The longitudinal two dimensional models cannot be used to examine the effects of the electrode shape and thickness regarding heat generation during the seam welding process. The transversal two dimensional models are not helpful for examining the nugget growth during the seam welding process. The heat energy generated during the seam welding process mainly depends on the resistance between the electrodes, welding current, rotational speed and the geometry of the electrodes. The settings for appropriate parameters in relation to a seam welding machine, with regards to sheets of different thicknesses, depends on trial and error methods. These methods are expensive and time consuming. The three dimensional model developed in this paper is a step towards selecting the appropriate welding parameters so as to produce a good welding nugget.