Hitachi RAM-60QH4 Manuel De Service page 100

• R107, R106 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.)
0
G
0
[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-60QH4, starting current control is performed by software.
• Starting current will change reflect to change in power voltage. This control system deals with change in voltage as
shown below.
(1) As shown in Fig. 8-6, U
(2) As shown in Fig. 8-7, ON time of W
about 10A.
+ and V - transistors on power module are turned on to apply current to winding of motor.
+ transistor changes according to DC voltage level so that starting current is
System power module
DC current
＋
U
DC 330V
−
U
Detection
resistor
Fig. 8-6
Chopper duty; large
10.0
7.5
5.0
2.5
Rotation speed
Fig. 8-5
＋ ＋
V
W
−
−
V
W
DC current (starting current)
Start
Fig. 8-7
– 112 –
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: 330V
DC voltage: High
Set value
Time