Software controlled medium frequency DC spot welding system design and implementation

Resistance spot welding (RSW) is one of the widely preferred resistance welding methods in today's mass production conditions. Medium frequency direct current (MFDC), on the other hand, is an efficient and advanced technology with more accurate current results compared to the alternating current (AC) method. In this study, a cost-effective medium frequency (MF) inverter designed and realized that can be used in MFDC-RSW systems. In addition, a computer interface that provides control of the welding cycle is designed and the inverter is controlled through this interface program. An MFDC-RSW experimental setup was created to test the performance of the MF inverter. The MF voltage generated in the inverter was applied to the MFDC weld transformer with a rated power of 175 kVA. MFDC weld current from the full-wave rectifier mounted on the secondary of the transformer was applied to a flexible copper busbar, which was determined as the load. For closed loop current control of the inverter, current information is taken from Rogowski coil (RC) wound on the flexible busbar. In the test results, the welding current defined in the welding control interface could be applied to the load without any significant difference. Root mean square error (RMSE), which was found to be 0.178 kA in the without feedback control operation, decreased in the feedback control studies. RMSE decreased to 0.109 kA when RC was connected in straight and 0.113 kA when connected in reverse. It is thought that the realized MF inverter has the potential to be used as an interface for closed loop MFDC current control in MFDC-RSW applications. It can be said that the total cost of the inverter is more suitable than its alternatives. It is expected that this study will contribute to the improvement of the weld current in the control of MFDC-RSW systems.