Hitachi RAC-18WSPA, Service Manual

Page: 64 / 101

Fig. 7-3 Voltage waveform at each point
U transistor chopped
Chopping period (208
嘕
sec.)
Chopping period
T
transistor ON
U
280V-300V
Voltage at V V
Upper arm transistor
Current at
ON
+
-
A
B
V
Time
W
T
V
U
V
Upper arm
transistor
Lower arm
transistor
W W
U
E F
+ +
W
+ +
- -
V
-
Fig. 7-2 Switching order of power module
Intelligent power module switches power supply current according to position of the compressor motor
rotor.
The switching order is as shown in Fig. 7-2.
At point ( : U+ is ON, V- is ON (circuit in Fig. 7-1)
At point ) : U+ is chopped (OFF), V- is ON (circuit in Fig. 7-4)
Upper arm transistor is controlled to ON/OFF by 2.5kHz-5kHz chopper signal. Rotation speed of the
compressor is proportional to duty ratio (ON time/ ON time + OFF time) of this chopper signal.
Time T in Fig. 7-2 shows the switching period, and relation with rotation speed (N) of the compressor is
shown by formula below;
N = 60/2 X 1/T
Fig. 7-3 shows voltage waveform at each point shown in Figs. 7-1 and 7-4. First half of upper arm is
chopper, second half is ON, and first half of lower arm is chopper, second half is ON.
When power is supplied U+ V- , because of that U+ is chopped, current flows as shown below;
(1) When U+ transistor is ON: U+ transistor U coil V coil V- transistor DC current detection
resistor Point % (Fig. 7-3)
(2) When U+ transistor is OFF: (by inductance of motor coil) U coil V coil V-transistor
U- diode Point
$
(Fig. 7-4)