Hitachi RAM-40QH5 Service Manual page 52

R500 and R253, detect DC current in current circuit. Microcomputer compensates for overload set value
G
so that the following is obtained:
DC voltage: High → DC current: Low
{
DC voltage: Low → DC current: High
(Since load level is expressed by DC voltage x DC current, this is intended to perform the same load
judgement even when the voltage varies.)
0
0
[When starting current control]
It is necessary to keep starting current (DC current) fixed to ensure smooth starting of DC motor for
G
compressor.
For RAM-40QH5, starting current control is performed by software.
G
Starting current will change reflect to change in power voltage. The control system deals with change in
G
voltage as shown below.
(1) As shown in Fig. 8-6, U
of motor.
(2) As shown in Fig. 8-7, ON time of W
current is about 10A.
DC 360V
Chopper duty: large
10.0
7.5
5.0
2.5
+ –
and V transistors on power module are turned on to apply current to winding
+
DC current
U +
U —
Detection
resistor
Start
Rotation speed
Fig. 8-5
transistor changes according to DC voltage level so that starting
System power module
V + W +
V — W —
Fig. 8-6
DC current (starting current)
Fig. 8-7
– 58 –
Amplification rate : low
DC voltage : low
DC current : high
Amplification rate : x 7.3
DC voltage : 230V
Amplification rate : high
DC voltage : high
DC current : low
Compressor motor
U
V
W
DC voltage: low
DC voltage: 360V
DC voltage: high
Set value
Time