– 80 –
(2) Overload control circuit (OVL control circuit)
●
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 judgement by comparing the DC current level and set value.
●
Fig. 8-4 shows the overload control system configuration and Fig. 8-5 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 micro
computer software with the DC current value.
Judgement OVL
with respect to
externally set
value
A/D
converter
A/D
converter
Judgement OVL
according to the rotation
speed
Selects data according
to the rotation speed and
DC voltage
OVL start current data
Motor control
process
Detection
resistor
To power module
negative terminal
DC current
(R806)
Overload
externally set
value circuit
Voltage amp.
circuit
(External judgement)
(Internal judgement)
DC voltage
AX-8E21 Micro computer
-
Rotation speed data
Fig. 8 - 4 Overload Control System Configuration
External judgement value
Judgement value according to the rotation speed
(internal judgement value)
Rotation speed
DC current
Fig. 8 - 5
1
. Overload external judgement circuit
●
The filter consisting of R320 and C1 removes high harmonic components from the voltage generated by
the current flowing to R806, R2 and C304 average the voltage. This voltage is then input to OP1 pin
5
and amplified and is supplied to micro computer pin
@
which is comparedwith the voltage at pin
#
. If the
voltage at pin
@
is higher than that at pin
#
, the micro computer enters the overload control mode.
●
Fig. 8-7 shows the rotation speed control. When the voltage at pin
9
of HIC exceeds the set value at pin
HIC
8
, the micro computer decreases the rotation speed of the compressor and reduces the load
regardless of the rotation speed commanded by the indoor micro computer.
