Research On The AC Inverter Spot Welding Power Supply

Currently, the single-phase AC resistance welding power supply is one of the resistance welding equipments widely used at home and abroad. The single-phase AC resistance welding power supply provides alternating current which is similar with the sine-wave. However, it exists zero-crossing of welding current during welding, and the temperature discontinuously rises in workpiece. Therefore, the thermal efficiency is not so good. In addition, the AC wave forms with higher peak values and easily occurs splash on the workpiece. Inverter-controlled resistance welding machine is the mainly developing direction of resistance welding machine in the world today. Generally, the secondary rectification is necessary for it, but some troubles are caused by the secondary rectifying components. The price of the secondary rectifying components is expensive, and many other measures must be adopted to avoid the damage of the secondary rectifying components caused by overcurrent and overvoltage, which leads to the increase of complexity and cost. Thus, AC inverter spot welding power supply has been studied in order to solve the above problems.In this study, the hardware and the software systems of the AC inverter spot welding power supply are designed. The main circuit is made up of welding transformer, and full-bridge inverter in which 4 IGBT is adopted. The peak value of weld current is real-time measured by the control system. The results of measurement are sent to MCU to carry out A/D conversion and PI control. The results of PI control are used to adjust pulse width in order to obtain steady current. Meanwhile, the control system has fault diagnosis and protect function, such as overcurrent, overheat, and parameter monitor. The hardware circuit and software program are debugged after designing, and the no-load debugging and load debugging of main circuit are carried out.The AC inverter spot welding power supply adopts pulse-width modulation technology to control duty ratio and PWM pulses, which can speed up current commutation, cut down the zero-crossing time and improve the thermal efficiency. In addition to the advantageous feature of this type power supply which causes less Peltier effect in welding. The system can effectively control the current peak by controlling primary current, which can decrease splashing to some extent. The system can improve the disadvantages of current intermittent, slow response speed of current.