Hitachi RAS-E10H2 Service Manual page 46

Intelligent power module switches power supply current according to position of the compressor motor
rotor.
The switching order is as shown in Fig. 3-2.
Upper arm
transistor
Lower arm
transistor
Upper Upper arm transistor is controlled to ON/OFF by 2.5kHz - 5kHz chopper signal. Rotation speed of
the compressoris 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
isshown by formula below;
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.
U
V Voltage at Voltage at
A ◯
◯ ◯
280V-300V
Upper arm transistor Upper arm transistor Upper arm transistor Upper arm transistor
Current at
B ◯
◯ ◯
When power is supplied U
(1) When U + transistor is ON: U
detection resistor → Point B (Fig. 3-3)
(2) When U + transistor is OFF: (by inductance of motor coil) U coil → V coil → V
U diode diode → Point A (Fig. 3-4)
– – –
+
At point E : U is ON, V
At point F : U + is chopped (OFF), V
+ +
V
- -
U
Fig. 3-2 Switching order of power module
N = 60/2 X 1/T
+
transistor chopped
Chopping period
Chopping period (208µ sec.)
ON
Fig. 3-3 Voltage waveform at each point
+ → V , because of that U
–
+ transistor → U coil → V coil → V
is ON (circuit in Fig. is ON (circuit in Fig. 3-1) is ON (circuit in Fig. is ON (circuit in Fig.
– – –
is ON (circuit in Fig. is ON (circuit in Fig. 3-4) is ON (circuit in Fig. is ON (circuit in Fig.
– – –
E E F F
+ + +
W W W W U
- -
V V V
T
-
transistor ON
U
T
+ is chopped, current flows as shown below;
- 50 -
3-1)
3-4)
+
V
-
W
transistor transistor → DC current
– – –
transistor transistor
– – –
Time
→