– 87 –
● R500 and R253 detect DC current in current circuit. Microcomputer compensates for overload set value
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
judgment even when voltage varies.)
[When starting current control]
● It is necessary to keep starting current (DC current) fixed to ensure smooth starting of DC motor for
compressor.
● For RAM-50CNHZ2, starting current control is performed by software.
● Starting current will change reflect to change in power voltage. The control system deals with change in
voltage as shown below.
(1) As shown in Fig. 8-6, U
+
and V
-
transistors on power module are turned on to apply current to winding
of motor.
(2) As shown in Fig. 8-7, ON time of W
+
transistor changes according to DC voltage level so that starting
current is about 10A.
Fig. 8-5
DC current
0
0
Rotation speed
Amplification rate : low
DC voltage : low
DC current : high
Amplification rate : high
DC voltage : high
DC current : low
Amplification rate : x 7.3
DC voltage : 230V
U
+
U
—
V
+
V
—
W
+
W
—
U
V
W
Compressor motor
DC current
System power module
DC 360V
Detection
resistor
Fig. 8-6
Fig. 8-7
10.0
7.5
5.0
2.5
DC current (A)
W transistor
ON-time
Start
DC current (starting current)
Set value
Time
Chopper duty: large
DC voltage: low
DC voltage: 360V
DC voltage: high
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