Inverter MIG Welding control side..(help)

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Hi everybody,I have some question about mig.I have designed MMA welding machine and it is working well, all things is wonderfull in MMA mode.and then i want to design MIG machine and i changed control circuit because you know MMA is current control, MIG is Voltage control. And my circuit is same i only changed feedback side(When MMA mode, i take output current as feedback. when MIG mode, i take Output voltage as feedback). so i have some problems in this mode because sometimes my MIG machine's igbts explode.and i dont know why they explode..may be i have to change control side but i dont know....are there anybody to have any idea why it is exploding?Thanks everybody.
Reply:Are experiencing this trouble in short circuit transfer or spray transfer? if it is during short circuiit transfer, CV units control the maxium amount of amperage available during the "short circuit".
Reply:What brand unit is it?  Is this something you converted?Esab Migmaster 250Lincoln SA 200Lincoln Ranger 8Smith Oxy Fuel setupEverlast PowerPlasma 80Everlast Power iMIG 160Everlast Power iMIG 205 Everlast Power iMIG 140EEverlast PowerARC 300Everlast PowerARC 140STEverlast PowerTIG 255EXT
Reply:Originally Posted by weldingliferAre experiencing this trouble in short circuit transfer or spray transfer? if it is during short circuiit transfer, CV units control the maxium amount of amperage available during the "short circuit".
Reply:Two things, Look at your gate pulses. Make sure you have a dead spot between the two pulses. You want to make sure that in no way, can both IBTs can be turned on at the same time. If both are turned on at the same time it put a dead short across the DC buss and things go bang. The major welder manufacturers use both current and voltage feed back in the inverter and large transformer welders. You use the voltage feed back like you are tring to do. But they use the current feed  back to control the max current. When the mig wire shorts to the work, it may be possible to draw more current than the IGBTs can handle.The over heated IGBT may not want to turn off. You will want to design a circuit that will control the max on time. either by hard limiting the pulse width or using the current feed back to limit the max on time.      max on time = max current.Look at your design of output filters. mig and stick use different values of capacitors and inductance. If the pulse generator is a micro controller. You can bend the pulses to create inductance, Both miller and lincoln and esab and others do this with their micro controller inverter welders.
Reply:it is during short circuiit transfer
Reply:Originally Posted by ccawgcTwo things, Look at your gate pulses. Make sure you have a dead spot between the two pulses. You want to make sure that in no way, can both IBTs can be turned on at the same time. If both are turned on at the same time it put a dead short across the DC buss and things go bang. The major welder manufacturers use both current and voltage feed back in the inverter and large transformer welders. You use the voltage feed back like you are tring to do. But they use the current feed  back to control the max current. When the mig wire shorts to the work, it may be possible to draw more current than the IGBTs can handle.The over heated IGBT may not want to turn off. You will want to design a circuit that will control the max on time. either by hard limiting the pulse width or using the current feed back to limit the max on time.      max on time = max current.Look at your design of output filters. mig and stick use different values of capacitors and inductance. If the pulse generator is a micro controller. You can bend the pulses to create inductance, Both miller and lincoln and esab and others do this with their micro controller inverter welders.