Hitachi RAS-25CNH2 Service Manual page 47

DC 260-380V is input to power module and power module switches power supply current according to
G
rotation position of magnet rotor. The switching order is as shown in Fig. 3-2.
Upper arm
transistor
Lower arm
transistor
Upper arm transistor is controlled to ON/OFF by 3.2kHz chopper signal. Rotation speed of the compress
G
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
G
shown by formula below;
Fig. 3-3 shows voltage waveform at each point shown in Figs. 3-1 and 3-4.
G
Voltage between
and
A B
260V-380V
Upper arm transistor
current at
B
When power is supplied U + [ U – , because of that U + is chopped, current flows as shown below; B
G
(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)
[
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)
+
V W
W – U –
Fig. 3-2 Switching order of power module
N = 60/2 X 1/T
U transistor chopped +
Chopping period
Chopping period (313 µ sec.)
ON
Fig. 3-3 Voltage waveform at each point
E F
+ +
U
V –
T
U transistor ON
T
– 50 –
]
+
V
W – U –
Time