Hitachi RAS-50FH5 Service Manual page 66

DC 260-360V is input to system power module and system power module switches power supply current
according to rotation position of magnet rotor. The switching order is as shown in Fig. 3-2.
Upper arm
transistor
Lower arm
transistor
Upper arm transistor is controlled to ON/OFF by 3.3kHz chopper signal. Rotation speed of the compress
is proportional to duty ratio (ON time/ ON time + OFF time) of this chopper signal.
Time T in Fig. 3-2 shows the switching period, and relation with rotation speed (N) of the compressor is
shown by formula below;
Fig. 3-3 shows voltage waveform at each point shown in Figs. 3-1 and 3-4. First half of upper arm is
chopper, second half is ON, and first half of lower arm is chopper, second half is ON.
Voltage at
A
260V-360V
Upper arm transistor
Current at
B
When power is supplied U
+
(1) When U transistor is ON: U
resistor
+
(2) When U transistor is OFF: (by inductance of motor coil) U coil
diode Point
[
+
At point E: U is ON, V
+
At point F: U is chopped (OFF), V
+
V
U Ð
Fig. 3-2 Switching order of power module
N = 60/2 X 1/T
+
U transistor chopped
Chopping period
ON
Fig. 3-3 Voltage waveform at each point
+ Ð
U , because of that U
+
transistor
Point (Fig. 3-1)
B
(Fig. 3-4)
A
Ð
is ON (circuit in Fig. 3-1)
Ð
is ON (circuit in Fig. 3-4)
E F
+ +
W U
V Ð
T
-
U transistor ON
T
+
is chopped, current flows as shown below;
U coil V coil
– 78 –
]
+
V
W Ð
Ð
V transistor DC current detection
Ð
V coil V transistor
Time
B
Return