●
DC 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 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
1/T
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.
●
When power is supplied U
+
U
-
, 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. 3-1)
(2)When U
+
transistor is OFF: (by inductance of motor coil) U coil V coil V
-
transistor Returm
diode Point (Fig. 3-4)
［
［
×
→
→
→
→
→ → →
→ → →
U transistor chopped
Chopping period(313
μ
sec.)
Chopping period
T
transistor ON
V
Time
W
T
Fig. 3-2 Switching order of power module
Fig. 3-3 Voltage waveform at each point
V
U
V
Upper arm
transistor
Lower arm
transistor
W
U
EF
◯
B
◯
A
U
320-360V
Voltage between
Upper arm transistor
Current at
ON
++
+
++
-
-
--
- 288 -
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