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E-4E-4

THEORY OF OPERATION

FIGURE E.3 MAIN TRANSFORMER

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INPUT

INPUTRECTIFIER LINE

SWITCH

"A"

L

E

A

D

FAN

MOTORS

R

E

C

O

N

N

E

C

T

S

W

I

T

C

H

18VAC

POWER BOARD

MAIN

 

TRANSFORMER

 

 

 

 

CR1

 

 

 

RELAY

 

 

 

IGBT

 

 

 

 

 

 

POSITIVE

CAPACITOR

 

 

OUTPUT

 

 

 

TERMINAL

IGBT

 

 

 

IGBT

 

SHUNT

 

 

 

 

 

CURRENT

 

 

 

TRANSFORMER

 

NEGATIVE

 

 

 

CAPACITOR

 

F

OUTPUT

 

 

TERMINAL

 

 

E

F

IGBT

 

E

E

 

 

D

E

 

 

B

D

 

 

A

B

 

 

C

A

O

 

K

C

V

 

 

E

 

THERMOSTATS

K

R

 

 

V

 

 

 

O

 

 

 

L

 

 

 

T

IGBT GATE SIGNALS

THERMAL

A

G

 

 

E

PROTECTION SIGNAL

CONTROL BOARD

LIGHT

 

CR1 RELAY DRIVE SIGNAL

 

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AUXILIARY

TRANSFORMER

REMOTE

RECEPTACLE

OUTPUT STRIKE ARC

 

 

 

LOCAL/

 

MODE

 

REMOTE

CONTROL CONTROL FORCE

SWITCH

CONTROL

 

 

 

SWITCH

 

 

 

 

MAIN TRANSFORMER

Each IGBT pair acts as a switch assembly. Each assembly feeds a separate, oppositely wound primary winding of the main transformer. The reverse direc- tions of current flow through the main transformer pri- maries and the offset timing of the IGBT pairs induce an AC square wave output signal at the secondary of the main transformer.

The DC current flow through each primary winding is redirected or “clamped” back to each respective filter capacitor when the IGBTs are turned off. This is needed due to the inductance of the transformer pri- mary winding.

The primary currents also pass through the current transformer which sends a signal to the control board. If the primary currents are not equal the control board compensates by adjusting the IGBT gate signals.

The firing of both IGBT pairs occurs during halves of the 50 microsecond intervals, creating a constant 20 KHZ output.

NOTE: Unshaded areas of block logic diagrams are the subject of discussion.

INVERTEC V250-S

Page 28
Image 28
Lincoln Electric V250-S service manual Figure E.3 Main Transformer