Hitachi RAM-60QH4 Manuel De Service page 80

DC 300-330V 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
Lower arm
transistor
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;
N=60/2 1/T
Fig. 3-3 shows voltage / current 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.
U
Voltage point
◯ A
300-330V
Upper arm transistor
Current at ◯ B
When power is supplied U +
●
(1)When U + transistor is ON: U + transistor
resistor → Point
(2)When U + transistor is OFF: (by inductance of motor coil) U coil
diode Point (Fig. 3-4)
→
+
V
-
U
Fig. 3-2 Switching order of power module
×
+
transistor chopped
Chopping period
Chopping period
ON
Fig. 3-3 Voltage waveform at each point
U - , because of that U + is chopped, current flows as shown below;
→
→
(Fig. 3-1)
E F
+ +
U
W
-
V
T
-
transistor ON
U
T
V - transistor
U coil V coil
→ →
→
– 92 –
［
+
V
-
W
DC current detection
→
V - transistor
V coil
→ →
Time
Return