An Asymmetrical Soft-switching Inverter

The phase-shifted soft switch topology has a shortcoming whose load scope is so narrow that it can't be competent for welding. On analyzing of arc power source topology, a phase-shifted soft-switch topology is put forward to make the lead arm turn off on zero voltage and lag arm turn off on zero current in this paper. By adding an auxiliary circuit to the secondary side of transformer ,the optimized topology can work in no load,light load,full load and short-circuit and solve the problem of applying the phase-shifted soft switch technology to welding.And on the IGBT mode,the method of calculating the paralle capacitor and the blocking capacitor is presented.The main circuit of inverter adopts bridge structure which consists two parts.the lead arm and the lag arm and works on the mode of PWM.The lead arm is paralle with high capacitor and the lag arm with low value and the two arms work alternately.The output power depends on duty circle of the lead arm and the lag arm is not regulated. The voltage on the lead arm capacitor rises so slowly that the lead arm works on zero voltage turn-off mode. The resonance loop consists of saturated inductor and blocking capacitor.The saturated inductor can keep the loop energy steady to reduce the loss of the duty cycle ;the blocking capacitor can reduce the power loss causing by circle current and turn-off loss and the lag arm works mainly on the zero current turn-off mode . The lead arm works on the zero voltage mode. With the blocking effect of the saturated inductor.the initial current in the primary coiling of transformer is low ,so the lag arm works on the zero current mode when turned on.So,in conclusion, the load works on the soft-switch mode.In phase-shifted soft-switch circuit, the parallel capacitor must be completely discharged during work process;otherwise, the capacitors in parallel connection with the lead arm will be short by IGBT turned on, so IGBT will be broken. There are many states such as no load,load,short-circuit etc. in welding and the current phase-shiftedsoft-switch circuit can not work on soft-switch mode in all load.An auxiliary circuit is designed,which can supply a reactive current to make the capacitors parelle connection with the IGBT discharged completely in light and no load and realize soft switch mode.So,the phase-shifted soft-switch circuit can be applied to the welding power source to improve their efficiency and reliability.The research has been applied to many welding machines,such as manual arc welding,gas arc welding and Submerged arc welding ,and so on.And it gets much more achievement on then manufacture of skip, the construction of power station and steel structure project.The common inverter has input rectifying diode and filter electrolytic capacitor to turn the AC into DC.The circuit has such shortcomings as can cause electric grid peak current whose interfere to the electric grid is strong. Because it is complex and costly,three-phase active PFC rectifier can not be used in welding power source nowadays. According to welding characteristics and technics,a single stage three-phase PFC rectifier is put forward in which the voltage signal of the electric grid is introduced into the feedback loop of the inverter peak current to compensate the input current,so the PFC is improved which can reach 0.95 in full load and the harmnic is reduced whose 5th harmic reduce from 55 % to 20%.The control mode of the welding inverter can be divided into two groups :the voltage mode and the current mode. The peak current mode can prevent the transformer from bias magnet and the switching device from failing causing by overcurrent but it is easy to be interfered.On studying the peak current close loop feedback,the slope compensate signal is introduced into the feedback loop to prevent duty circle from tingling and increase the steability of the close loop current. According to the interfere the diode inverse recovery current opposed on the peak current loop, an inverse recovery current elimination circuit is designed to screen the current front edge of t...