High power, unity power factor supply for plastic pipe welding applications

The paper describes a 3kW single phase switched mode power converter operating with unity power factor for welding plastic pipes. The pipe Joints contain a fine wire that is heated electrically to melt the plastic and form the bond. For quality reasons, the Joints are rated for 50Hz ac operation, where movements in the wires due to the ac. power supply cause mixing of the molten plastic and hence high joint integrity. Here, the output of the converter must Provide a rectified 50Hz wave-shape to avoid the necessity for re-qualification of the existing joints for DC operation, where no wire vibration would occur. The paper shows the design, simulation of the operation and gives practical results from the supply.