Hitachi RAS-25CNH2 - Page 47

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● DC 260-380V 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.
E
F
UVVW
Upper arm
transistor
Lower arm
transistor
Time
++
T
+
+
T
W
–
W
–
U
–
U
–
V
–
U transistor chopped U transistor ON
ON
Voltage between
Upper arm transistor
current at
Chopping period
Chopping period (313
µ sec.)
and
260V-380V
A
+
B
B
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;
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.
Fig. 3-3 Voltage waveform at each point
● When power is supplied U
+
[ U
–
, because of that U
+
is chopped, current flows as shown below; B
(1) When U
+
transistor is ON: U
+
transistor [ U coil [ V coil [ V
–
transistor [ DC current detection
resistor [ Point B (Fig. 3-1)
When U
+
transistor is OFF: (by inductance of motor coil) U coil [ V coil [ V
–
transistor [ Return diode
[ Point A (Fig. 3-4)