Hypertherm Powermax900 Service Manual - Manual (Page 33)

M
AINTENANCE
3-6 Service Manual
Functional Description
Refer to block diagram 3-7, and the system wiring diagram. See Parts List Sections 4, 5 or 6: to
identify system components referenced in this description.
AC power enters power switch S1 from terminal block TB1. The MOV and filter capacitor block
MOV1 provides spike and noise suppression. A "soft start" is implemented via power board resistors
R1 and R2 and relay RL1, and the main contactor CR1. Once the capacitors on the power board are
charged up and incoming power is within limits, the control board turns on the main contactor. Diode
bridge D1 rectifies the AC to DC. The DC voltage is then supplied to the inverters.
Each inverter consists of several components: an isolated gate bipolar transistor (IGBT - Q1 or Q2), a
coil of the power transformer (T2), a current sense transformer (CS1 or CS2), and sections of the
power board. The inverters operate as a pulse width modulator controlled half-bridge circuit. The
inverters are capacitor fed and transformer coupled, switching at 20 KHZ. The inverter outputs are
connected in series, and are rectified by output diodes D2 and D3.
The output circuitry consists of a current sensor CS4 and transfer sensor CS3 located on the control
board, pilot arc relay CR2, and output inductor L1.
The feedback loop operates as follows: The amp adjust pot P1 is first set to the desired value.
Current sensor CS4 measures the actual output current and compares it at the error amplifier with the
user-set current setting. The error amplifier output is an analog indication of how wide the pulse width
should be to maintain the current setting. The error amplifier output is then fed to the pulse width
modulator chip PWM. The pulse width modulator sends the signal to the gate drive board
transformers, and the gate drive boards in turn drive the inverter IGBTs Q1 and Q2.
Gate Drive Xfrmr
on Q2 Gate Drive Xfrmr
on Q1
PWM
Error
Amp. +
–
P1 Control PCB
Power On
LED
Line
Voltage
LED
Temp
LED
Gas
Pressure
LED
Gas Test
Switch
D1
+
–
INVERTER 1
(Q1, CS1, T2
Power PCB)
INVERTER 2
(Q2, CS2, T2
Power PCB)
T2
T2
TB3
AC In TB1 S1
MOV1
CR1
R1,R2,
RL1
Power
PCB
TB2
Control
Xfrmr
T1
Fan
M1
+
–
D2, D3
L1
Current
Sensor
CS4
Xfer
Sensor
CS3
CR2
RC Filter
PowerPCB
Control PCB
Work
Torch
Nozzle
Filter/
Regulator
Gas/Air
Supply
Torch Start
Cap Sensor
Solenoid
V1
Pressure
Switch PS1
Figure 3-7 Single-Phase, 200/208/230/240 Block DIagram