Hitachi RAS-25CNH2 Service Manual page 60

R507, R508, R5 detect the DC voltage at the power circuit. The micro computer receives a DC voltage
G
(260-380V) via HIC
when the DC voltage is high (low).
(Since the load level is indicated by the DC voltage multiplied by DC current, R229, R230, R231 are
provided to perform the same overload judgement even when the voltage varies.)
< During start current control >
It is required to maintain the start current (DC current) constant to smooth the start of the DC motor for
G
the compressor.
The RAC-25CNH2 uses software to control the start current.
G
The start current varies when the supply voltage varies. This control method copes with variations in the
G
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 Fig8-9.
(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. 8-10.
DC 260-380V
Chopper duty: high
20
15
10
5
0
O
and applies correction to the overload set value so the DC current is low (high)
G 0 0
DC current
U +
U –
Detection
resistor
Start
Rotation speed
Fig. 8-8
Power module
V + W +
V – W –
Fig. 8-9
DC voltage (start current)
Fig. 8-10
– 63 –
Amplification : low
DC voltage : low
DC current : high
Amplification : 8.5 times
DC voltage : 260V
Amplification : high
DC voltage : high
DC current : low
Compressor motor
U
V
W
DC voltage: low
DC voltage: 280V
DC voltage: high
Set value
Time