Hitachi RAF-35NH5 Service Manual page 258

C 320-360V is input to power module and power module switches power supply current according to rotation
●
position of magnet rotor. The switching order is as shown in Fig. 3-2.
At point E: U + is ON, V - is ON (circuit in Fig. 3-1)
［
At point F: U + is chopped (OFF), V - is ON (circuit in Fig. 3-4)
Upper arm
transistor
Lower arm
transistor
Upper arm transistor is controlled to ON/OFF by 3.2kHz 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;
N=60/2
Fig. 3-3 shows voltage waveform at each point shown in Fig. 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.
U transistor chopped
Voltage between
A
⃝
320-360V
Upper arm transistor
Current at
B
⃝
When power is supplied U +
●
(1)When U + transistor is ON: U + transistor
resistor Point
→
(2)When U + transistor is OFF: (by inductance of motor coil) U coil
diode Point (Fig. 3-4)
→
+
V
-
U
Fig. 3-2 Switching order of power module
1/T
×
+
Chopping period
Chopping period(313
ON
Fig. 3-3 Voltage waveform at each point
U - , because of that U + is chopped, current flows as shown below;
→
→
(Fig. 3-1)
E F
+ +
U
W
-
V
T
-
transistor ON
U
T
sec.)
μ
V - transistor
U coil V coil
→ →
→
- 288 -
［
+
V
-
W
C current detection
→
V - transistor
V coil
→ →
Time
Returm