Research On Soft Switching Resistance Spot Welding Inverter

As an important branch in the field of the resistance-welding,spot welding inverter has many advantages compared with the traditional spot welding power sources.With soft-switching technology, spot welding inverter has lower switching dissipation,lower electromagnetic interference and lower sensitivity to the parasitic parameters of power circuit, which fundamentally improved the system output characteristics, and circuit efficiency stability and reliability.The paper analyzed the principle of the Zero-Voltage-Switching PWM DC/DC full bridge converter with assistance network, as well as the Zero-Voltage-Zero-Current-Switching PWM DC/DC full bridge converter with blocking capacitor. The Simulink module in MATLAB software is used for circuit simulation, including the soft-switching process of the leading arm and lagging arm,working waveforms of the power transformer and process of rectifier and transition.The influence of the filter capacitor, the resonant inductance of inverter circuit and variation of load to the system were discussed. Hardware was designed, including the rectifier filter circuit, IGBT full bridge inverter circuit and the PWM trigger circuit based on UCC3895 and IR2110. Control circuit with AT89C51 as a core was devolopped, including the display and keyboard management circuit based on ZLG7290, AT24C02 serial data memory circuit. Relevant software was designed, including system main program, phase-shifted PWM program, keyboard management program, and welding time sequence program.Simulation results and experiment results showed that:(1)Filter capacitor selection should ensure the output current of the rectifier circuit is intermittent pulse, rectifier and filter capacitor supply power to the load alternatively between peaks and troughs of the voltage,and now the output voltage is relatively smooth.When the filter capacitor is small, the output current of rectifier is positive with little fluctuation,and now the output voltage is similar to the output of full-wave rectifier without filter capacitor which fluctuate dramatically;(2)In ZVS circuit,it easily fufils soft-switching condition in lagging arm as leakage inductance of power transformer increases,but bigger leakage inductance of power transformer increases opening dissipation of transformer and decreases efficiency of soft-switching inverter power source;(3)In ZVZCS circuit,the transformer leakage inductance can not be too large,otherwise the time of primary side current from peak to zero will increase,and the soft-switching range of lagging arm will decrease.In the condition of keeping the blocking capacitor costant and lagging arm can achieve ZCS,the larger value of the transformer leakage inductance,the higher peak voltage of the lagging arm IGBT.