Fullwave Frequency Converter (FWFC) Welding Control for Resistance Welding
The fullwave frequency converter control is similar in design to the mid frequency system (MFDC). The significant difference is in the fact that this system generates frequencies below that of the base frequency. Instead of using IGBTs for pulsing the welding transformer, the FWFC control utilizes SCRs for inputs 1 through 4.
These SCRs are simply used for directional control of current; passing current either from 4 to 1, or from 2 to 3. There are six other SCRs which are used for creating a DC charge across a bus. This is similar to that of the MFDC system which uses diodes instead. The reason for the use of SCRs in the FWFC system for producing the DC power is that these SCRs are gated every half cycle for the duration of the weld and can be turned off by the zero crossing of the three phase power when gating current is no longer applied. This way, the SCRs that are used for directional control at positions 1 through 4 will also turn off.
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