– 142 –
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.)
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.
<During start current control>
0
5
10
15
20
0
Rotation speed
Fig. 7-8
Fig. 7-9
Fig. 7-10
0
G
Amplification : low
DC voltage : low
DC current : high
Amplification : high
DC voltage : high
DC current : low
Amplification : 8.5 times
DC voltage : 320V
W
U
V
W
V
U
U
V
W
+
+
+
-
-
-
DC320-360V
DC current
Power module
Compressor motor
Detection
resistor
DC current
Chopper duty : high
Start
W transistor
ON-time
DC current(A)
DC voltage : low
DC voltage : 320V
DC voltage : high
DC voltage(start current)
Set value
Time
