– 78 –
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.
E
F
UVVW
Upper arm
transistor
Lower arm
transistor
Time
++
T
+
+
T
U
Ð
V
Ð
W
Ð
U transistor chopped
U transistor ON
ON
Voltage at
Upper arm transistor
Current at
Chopping period
260V-360V
A
+
-
B
At point E: U
+
is ON, V
Ð
is ON (circuit in Fig. 3-1)
At point F: U
+
is chopped (OFF), V
Ð
is ON (circuit in Fig. 3-4)
[]
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. 3-2 Switching order of power module
N = 60/2 X 1/T
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.
Fig. 3-3 Voltage waveform at each point
When power is supplied U
+
U
Ð
, because of that U
+
is chopped, current flows as shown below;
(1) When U
+
transistor is ON: U
+
transistor U coil V coil V
Ð
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
Ð
transistor Return
diode Point (Fig. 3-4)
A
B
B
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