Hitachi RAC-50DH7, Service Manual

Page: 63 / 101

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8. Overload control circuit (OVL control circuit)
Judgement value according to the rotation speed
(internal judgement value)
External judgement value
Detection
resistor
Translation
(R503)
DC current
Rotation speed data
To power module
negative
terminal
Primary
CT
0V
0V
Voltage amp.
circuit
Judgement OVL
with respect to
externally set
value
Judgement OVL
according to the rotation
speed
A/D
converter
OVL start current data
Selects data according
to the rotation speed and
DC voltage.
RC filter circuit
(Internal judgement)
DC voltage
DC
current
Rotation speed
Motor control
process
A/D
converter
A/D
converter
AX-6V01 micro computer
Fig. 8-1 Overload Control System Configuration
Fig. 8-2
●
Overload control is to decrease the speed of the compressor and reduce the load when the load on the
air conditioner increases to an overload state, in order to protect the compressor, electronic components
and power breaker.
●
Overloads are judged by comparing the DC current level and set value.
●
Fig. 8-1 shows the overload control system configuration and Fig. 8-2 is a characteristic diagram of
overload judgement values. There are two judgement methods-external judgement which compares the
externally set value with the DC current value regardless of the rotation speed and internal judgement
which compares the set value that varies according to the rotation speed programmed in the microcomputer
software with the DC current value.