– 122 –
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 4.76kHz 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 he 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 Return
diode Point (Fig. 3-4)
[
transistor chopped
Chopping period (313 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
E
F
B
A
320-360V
Voltage between
Upper arm transistor
Current at
ON
+
+
U
+
+
+
-
U
-
-
-
