Switching Order Of Power Module; Voltage Waveform At Each Point - Hitachi RAK-25NH4 Service Manual

DC 260-360V is input to system power module and system power module switches power supply current
according to 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 3.3kHz 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. 3-3 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.
Voltage at
A
260V-360V
Upper arm transistor
Current at
B
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
(2) When U + transistor is OFF: (by inductance of motor coil) U coil [ V coil [ V – transistor [ Return
diode [ Point
[
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
U –
Fig. 3-2 Switching order of power module
N = 60/2 X 1/T
+
U transistor chopped
Chopping period
ON
Fig. 3-3 Voltage waveform at each point
(Fig. 3-1)
B
(Fig. 3-4)
A
E
F
+ +
U
V –
T
-
U transistor ON
T
– 75 –
]
+
V
W –
Time
B