Efficiency improvements for high frequency resistance spot welding

Resistance spot welding uses direct current in the range of 1 kA to more than 100 kA to join sheet metals. The current is provided by an inverter that is connected a dc-link capacitor and transformer with a high turns ratio. The current is rectified at the secondary side of the transformer. Since the voltage between the tips of the welding electrodes is in the range of only a few Volts the voltage drop across the rectifier diodes contributes to high losses and therefore to a low efficiency. This paper presents a new high frequency transformer optimized for welding applications, which consists of submodules of planar transformers with integrated synchronous rectification, allowing size reduction and improved controllability of the welding process while reducing the transformer size and losses thus increasing the overall system efficiency. The potential of the new welding transformer is shown through experimental results.