Hitachi RAS-50WX8 Service Manual page 102

R500, R253, detect the DC voltage at the power circuit. The microcomputer receives a DC voltage (320-360V) via HIC
and applies correction to the overload set value so the DC current is low (high) when the DC voltage is high (low).
(Since the load level is indicated by the DC voltage multiplied by DC current, R247, R248, R249 are provided to perform
the same overload judgement even when the voltage varies.)
0
G
0
<During start current control>
It is required to maintain the start current (DC current) constant to smooth the start of the DC motor for the compressor.
The RAC-50FX8 uses software to control the start current.
The start current varies when the supply voltage varies. This control method copes with variations in the voltages as follows.
(1) Turns on the power module's U + and V - transistors so the current flows to the motor windings as shown in Fig.7-9.
(2) Varies the turn-On time of the W + transistor according to the DC voltage level and the start is controlled so the start
current is approx. 10A as shown in Fig.7-10.
Chopper duty : high
Rotation speed
DC current
+
U
DC320-360V
-
U
Detection
resistor
20
15
10
5
0
Start
Amplification : low
DC voltage : low
DC current : high
Amplification : 8.5 times
DC voltage : 320V
Amplification : high
DC voltage : high
DC current : low
Fig. 7-8
Power module
+
+
V W
U
V
W
-
-
V
W
Fig. 7-9
DC voltage(start current)
Fig. 7-10
– 142 –
Compressor motor
DC voltage : low
DC voltage : 320V
DC voltage : high
Set value
Time