Research On High Frequency Inverter Resistance Spot Welding Power Supply

With the development of the advanced manufacturing technology towards the direction of precision in our country, there has been a lot of welding processes of microelectronic devices, thin components and precision instruments. The welding of micro-components requires the welding power supply with high control accuracy and excellent dynamic characteristics, which makes high-frequency inverter resistance spot welding power supply become a development trend of resistance spot welding power supply. Currently the frequency of most inverter resistance spot welding supply is 1-4 k Hz, which has some disadvantages, such as the imprecise energy input control and time control. Therefore, micro-components cannot be welded or the welding quality cannot be guaranteed. So the high-frequency inverter resistance spot welding power supply has been designed to meet the requirements of micro-components welding.An overall solution of the power supply has been put forward in this paper. Full-bridge inverter was chosen as the topological structure of main circuit. High-frequency transformer and secondary rectifying circuit were designed. The control system based on DSP was designed, including feedback sampling circuit, protection circuit, switching control circuit, communication interface circuit and interactive interface circuit, etc., and the control circuit PCB was designed according to the design requirements. The programs of the PWM, A/D sampling, PI control, LCD display, key scan, etc. were written and debugged.An experimental platform was built to debug the power supply. PI parameters were set to realize the three feedback control modes: constant-current, constant-voltage and constant-power. Different output waveforms can be obtained by setting the welding parameters flexibly, which can meet a variety of welding occasions. The inverter frequency of power supply is 25 k Hz, which makes the output wave is more stable. Compared with the current waveform of medium-frequency inverter resistance spot welding power supply, the results show that the rise time of current waveform of high-frequency inverter resistance spot welding power supply significantly is shorter, and the current waveform is also flatter, it turns out that the power supply designed has better control accuracy and faster dynamic response. In addition, the duty ratio loss of the power supply was measured, the results show that there is a basic linear relationship between the duty ratio and output current. There is no obvious duty ratio loss under bipolar limited soft-switching PWM control. Some resistance spot welding experiments were finished with micro filament, and it could be completed with good welding effect within the short time. The results show that high frequency inverter resistance spot welding power supply basically satisfies the requirements of the welding of micro-components. Consequently the power supply has certain value in practical application.