240V AC to 30ish DC @ 40-200ish A
Here is an outline of how you might go about a project like this. To do this safely and successfully, you need quite a bit of knowledge and experience.

Develop complete specifications

Read the complete specifications for the example product and understand all of the specifications.

Input voltage, 1 or 3 phase, frequency

Output open-circuit voltage, operating current, operating voltage

Maximum output power: highest arc voltage X arc current

Duty cycle definition: Is it time drawing an arc divided by total operating time?

Average output power

Operator adjustments and selections: Read the operator’s manual for the example product and understand all of the adjustments and selections that the operator can make.

These are the sections and major components that need to be designed or selected:


Input Circuit Breaker
Rectifier: Rectifier module, heat sink, possibly a cooling fan
Filter: Capacitor or capacitor bank and possibly a charge current limiting mechanism
Inverter power unit: IGBT transistor module, heat sink, cooling fan
Transformer: Special 30 kHz transformer, probably a custom-made item in the example product, might need it’s own cooling fan
Rectifier: 30 kHz Rectifier module, heat sink, possibly a cooling fan
Inductor: Filters 30 kHz rectifier output and limits rapid output current changes
DC voltage and current transducers
PWM current and voltage control unit: This receives the operator selection and adjustment inputs, monitors the output voltage and current, compares the actual voltage and current with the operator selections and settings and the design limits, monitors the duty cycle, possibly monitors some internal temperatures and sends pulse width modulation (PWM) gate signals to the inverter to control the welder. It could probably be a single-board microcontroller that you would program to perform the required functions.
IGBT Gate signal driver: This receives signals from the control unit and provides isolated signals to the IGBT gates.
Operator input devices and miscellaneous items.