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Intelligent power module switches power supply current according to position of the compressor motor
rotor.
The switching order is as shown in Fig. 4-2.
Upper arm
transistor
Lower arm
transistor
Upper arm transistor is controlled to ON/OFF by 4.8kHz 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. 4-2 shows the switching period, and relation with rotation speed (N) of the compressor is
shown by formula below;
Fig. 4-3 shows voltage waveform at each point shown in Figs. 4-1 and 4-4. First half of upper arm is
chopper, second half is ON, and first half of lower arm is chopper, second half is ON.
U
Voltage at
A
280V-300V
Upper arm transistor
Current at
B
When power is supplied U
+
(1) When U
transistor is ON: U
detection resistor → Point B (Fig. 4-1)
+
transistor is OFF: (by inductance of motor coil) U coil → V coil → V
(2) When U
–
U
diode → Point A (Fig. 4-4)
+
At point E : U
is ON, V
+
At point F : U
is chopped (OFF), V
+
V
-
U
Fig. 4-2 Switching order of power module
N = 60/2 X 1/T
+
transistor chopped
Chopping period
Chopping period (208μ sec.)
ON
Fig. 4-3 Voltage waveform at each point
+
–
→ V
, because of that U
+
transistor → U coil → V coil → V
–
is ON (circuit in Fig. 4-1)
–
is ON (circuit in Fig. 4-4)
E
F
+
+
U
W
-
V
T
-
transistor ON
U
T
+
is chopped, current flows as shown below;
- 54 -
+
V
-
W
–
transistor → DC current
–
transistor →
Time
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