Medium frequency – Inverter

Medium-frequency welding is resistance welding using rectified medium-frequency alternating current, usually at 1000 Hz. The core of this is the inverter as the power source for the MF transformer with rectifier package.

The HWH inverters consist of the input contactor, a rectifier set (B6 bridge), the DC link capacitors and the actual inverter, an IGBT bridge circuit, as well as the monitoring and control electronics.

When the mains voltage is applied, the inverter carries out extensive self-test functions. The capacitor bank of the DC link is precharged via current limiting resistors. The safety contactor is then released. A DC voltage of approx. 550 V is now available to the inverter. By alternately switching the IGBTs on and off with variable pulse widths, this DC link voltage is converted into a single-phase AC voltage with a frequency of 1000 Hz.

The MF transformer then transforms this to the welding voltage. To eliminate the inductive reactance caused by the high frequency of 1000 Hz, high-current diodes are integrated into the transformer for rectification.

The actual welding control, now with a time base of 1 ms, is integrated in the inverter. The unit is operated either via a separate control panel or via a PC user interface.

MF welding combines all the advantages of classic direct current with the highest dynamics and control options.