New design method for controlling power stages based on IGBT switching ferrite transformers: applied to an 8 kW small size light weight electric welding machine

摘要

To solve the problem of weight (/spl sim/50 kg) and size (/spl sim/60 cm/spl times/40 cm/spl times/20 cm) of power electric welding machines, a new one was achieved. Working at high frequencies (/spl sim/80 kHz) with IGBTs switching ferrite transformers, its specifications were chosen for industrial application (50 V 160 A output, size of a small case and 5 kg maximum weight). This paper focuses on one problem which remained unsolved: immediate IGBT destruction when the conceived transformer was included in the circuit. By working below 50% duty cycle during switching, we were able to prevent the destruction of the IGBT and control the soldering arc. An interpretation of IGBT behavior leading to its destruction was deduced: after conduction of the IGBT, a constant current crosses it limited by the transformer inductive circuit without load. At cutoff strong instantaneous power amplifies the temperature overtaking its value limits leading to component destruction.