Theory of operation, Switch boards and main transformer – Lincoln Electric INVERTEC SVM199-A User Manual

Page 35

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THEORY OF OPERATION

SWITCH BOARDS AND MAIN
TRANSFORMER

There are two switch boards in the INVERTEC® V450-
PRO, each containing an input capacitor and insulated
gate bipolar transistor (IGBT) switching circuitry. Refer
to Figure E.3. When the machine reconnect switches
are configured for a lower input voltage (below 300
VAC) the input capacitors are connected in parallel.
When the machine is configured for higher input volt-
ages (300 VAC and above) the input capacitors are
connected in series.

When the input capacitors are fully charged they act as
power supplies for the IGBT switching circuit. The
Insulated Gate Bipolar Transistors switch the DC
power, from the input capacitors, “on and off” thus sup-
plying pulsed DC current to the main transformer pri-
mary windings. See IGBT Operation Discussion and
Diagrams
in this section.

E-3

E-3

INVERTEC® V450-PRO

FIGURE E.3 — SWITCH BOARDS AND MAIN TRANSFORMER

INPUT

CONTACTOR

INPUT

RECTIFIER

R

E

C

O

N

N

E

C

T

CONTROL BOARD

RIGHT

SWITCH

BOARD

LEFT

SWITCH

BOARD

MAIN

TRANSFORMER

CURRENT

SENSOR

CHOKE

OUTPUT

TERMINAL

OUTPUT

TERMINAL

POWER

BOARD

115VAC

RECEPTACLE

P

O

W

E

R

S

W

I

T

C

H

I

N

P

U

T

B

O

A

R

D

FAN

MOTOR

AUX.

TRANS.

AUX.

TRANS.

RECTIFIER

AUX.

RECONNECT

PRIMARY

CURRENT

SENSOR

WIRE FEEDER

RECEPTACLE

RS232

CONN.

THERMOSTATS

STATUS

LIGHT

THERMAL

LIGHT

CURRENT FEEDBACK

VOLTAGE FEEDBACK

65VDC

40VDC

CONTROL SIGNALS

PWM

DRIVE

CAPACITOR

VOLTAGE

FEEDBACK

CAPACITOR

VOLTAGE

FEEDBACK

PWM

DRIVE

VOLTAGE

SENSE

RECEPTACLE

#1

#2

S

W

I

T

C

H

INPUT

CONTACTOR

INPUT

RECTIFIER

R

E

C

O

N

N

E

C

T

CONTROL BOARD

RIGHT

SWITCH

BOARD

LEFT

SWITCH

BOARD

MAIN

TRANSFORMER

CURRENT

SENSOR

CHOKE

OUTPUT

TERMINAL

OUTPUT

TERMINAL

POWER

BOARD

115VAC

RECEPTACLE

P

O

W

E

R

S

W

I

T

C

H

I

N

P

U

T

B

O

A

R

D

FAN

MOTOR

AUX.

TRANS.

AUX.

TRANS.

RECTIFIER

AUX.

RECONNECT

PRIMARY

CURRENT

SENSOR

WIRE FEEDER

RECEPTACLE

RS232

CONN.

THERMOSTATS

STATUS

LIGHT

THERMAL

LIGHT

CURRENT FEEDBACK

VOLTAGE FEEDBACK

65VDC

40VDC

CONTROL SIGNALS

PWM

DRIVE

CAPACITOR

VOLTAGE

FEEDBACK

CAPACITOR

VOLTAGE

FEEDBACK

PWM

DRIVE

VOLTAGE

SENSE

RECEPTACLE

#1

#2

S
W
I
T
C
H

Each switch board feeds current to a separate, oppo-
sitely wound primary winding of the main transformer.
The reverse directions of current flow through the main
transformer primaries and the offset timing of the IGBT
switch boards induce an AC square wave output signal
at the secondary of the main transformer. These pri-
mary currents are monitored by the current transformer
(CT). If the primary currents become abnormally high,
the control board will shut off the IGBTs, thus disabling
machine output. The DC current flow through each pri-
mary winding is clamped back to each respective input
capacitor when the IGBTs are turned off. This is need-
ed due to the inductance of the transformer primary
winding. The firing of the two switch boards occurs
during halves of a 50 microsecond interval, creating a
constant 20 kHz output.

NOTE: Unshaded areas of Block Logic

Diagram are the subject of discussion

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