Switching Order Of Power Module; Voltage Waveform At Each Point - Hitachi RAS-25CNH1 Service Manual

DC 230V 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.
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;
Fig. 3-3 shows voltage waveform at each point shown in Figs. 3-1 and 3-4.
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
(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
U —
W —
Fig. 3-2 Switching order of power module
N = 60/2 X 1/T
U transistor chopped +
Chopping period
Chopping period
ON
Fig. 3-3 Voltage waveform at each point
E F
+ +
U
V —
T
U transistor ON
T
– 68 –
]
+
V
— U —
W
Time