Theory of operation, Main igbt inverter board – Lincoln Electric Invertec V205-T User Manual

Page 33

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MAIN IGBT INVERTER BOARD

The filtered input voltage, from the Input Board, is
applied through an input choke to the Main IGBT
Inverter Board. This input voltage is rectified, regulat-
ed and a unity power factor output is developed for
the main welding IGBTs. This unity power factor cir-
cuit provides several advantages over a traditional
bridge rectifier circuit. Among these advantages are
that the UPFR operates over a wide range of voltages,
there is no need for any manual circuit changes when
the input voltages are changed from 115VAC to
230VAC and there is absolute voltage stability main-
tained on the IGBT electrolytic capacitors. The four
main welding IGBTs are located on a large center
mounted heat sink assembly.

The pre-charge and auto reconnect circuits are posi-
tioned on the Main IGBT Inverter Board. When power
is first applied to the V205T the rectified DC input volt-
age is applied to the input capacitors through a cur-
rent limiting circuit. The capacitors are charged slow-
ly and current limited for approximately five seconds.
After five seconds a relay closes and the pre-charge
circuit is bypassed and a controlled DC input voltage
is applied to the weld capacitors and IGBTs making
them ready for welding output demands when the
IGBTs are gated on. The auto reconnect circuit
receives and processes a low-level voltage signal from
the Bus Board. This low level signal is utilized to

adjust for the different voltage requirements needed
by the weld IGBT circuits. A signal is also sent to the
Control Board so that when the input voltage is
reduced the output of the machine will be limited
accordingly.

The Auxiliary power portion of the board generates
several voltages through flyback topology and a
50KHZ switching frequency. These various voltages
(+24, +15, +5, +48 and –15) are utilized to operate the
control and protection electronics, the gas solenoid,
the trigger circuit and the fan motor.

The Main IGBT Inverter Board receives command and
pre-set signals from the Control/Display board. It also
receives feedback information, both voltage and cur-
rent, from the Output Filter Board and Hall Effect
Device via the Bus Board. It processes this informa-
tion and generates the correct pulse width modulation
signal (PWM) that is applied to the gates of the weld
IGBTs. This controls and regulates the output of the
machine. The thermostats signals are connected to
the Main IGBT Inverter Board. This status information
is passed on to the Control Board. In the case of an
over temperature condition the Control Board will pre-
vent output until the machine cools and the ther-
mostats reset.

Low-level analog signals are generated on the Main
IGBT Inverter Board and sent to the Control/Display
Board for meter set and actual display values.

THEORY OF OPERATION

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V205-T AC/DC