technical difference between CC and CV welder

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BEATMORTALITY

Joined: 26 Nov 2006
Posts: 2

04 Dec 2006 21:35 difference between igbt and regular welder

I am an electronics engineering student and
have recently completed my final semester. I have been trying to study the
designing of an inverter based welder but am stuck at a query which may
sound stupid to you but is of extreme importance to me.
My queries are listed below.
1: In an inverter based welder the IGBTs are switched at above 10 KHz
frequency, if I m right. If I want to design a CONSTANT CURRENT welder
using inverter technology WHAT ARE THE ISSUES THAT I HAVE TO TAKE CARE
OF. I WANT TO KNOW THE ISSUES RELATED TO THE CONTROLLING OF THE PULSES
(IGBT SWITCHING FREQUENCY) AND BASICALLY OTHER ISSUES RELATED TO THE
CONTROL CIRCUITARY.
Let me try to explain what I want to know about. Suppose I am
switching the IGBTs at a frequency of say 20 Khz and the duty-cycle of this
frequency is say 40%. If my welder can produce a maximum output of 400
Amps DC then it means that when there is a load of 400 Amps the IGBTs are
switching at 40% duty cycle (I hope this concept of mine is right). Now
if there is a load of only 100 amps then will my duty cycle reduce??
What is the other information u can give on what do I have to control
in a constant current welder.
Also I want similar information on a CONSTANT VOLTAGE welder. It
would be of great help if you could guide me with these issues
Regards.

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barfi

Joined: 11 Dec 2006
Posts: 40
Location: tehran

22 Dec 2006 18:00 difference between cv and cc?

I think the control scheme that you will use is not a concern (PWM you should use)
you only should consider some practical issues like Dead time between switching
time of transistors in each leg (you should use the half bridge or full bridge switching config. for this rating you had menttioned)
the other thing is the driving circuit of the IGBTS you maybe use an isolated
iGBT driver with high current capability for switching on the IGBTS like HCPL316
the other problem is the isolated current and voltage feedback circuits that for example you can use hall effect sensor for current and IL300 for voltage.
The biggest problem is the transformer design for this level of current and considering its efficiency you maybe should use ZVS or ZCS shcemes for switching your IGBTS and so on....