Hitachi RAC-25YH4, Service Manual, Page: 72 / 121

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280V-300V
Intelligent power module switches power supply current according to position of the compressor motor
rotor.
The switching order is as shown in Fig. 4-2.
At point E: U+ is ON, V is ON (circuit in Fig. 4-1)
At point F: U+ is chopped (OFF), V is ON (circuit in Fig. 4-4)
Fig. 4-2 Switching order of power module
Upper arm transistor is controlled to ON/OFF by 3.3kHz chopper signal. Rotation speed of the compressor
is proportional to duty ratio (ON time/ ON time + OFF time) of this chopper signal.
Time T in Fig. 4-2 shows the switching period, and relation with rotation speed (N) of the compressor is
shown by formula below;
N = 60/2 X 1/T
Fig. 4-3 shows voltage waveform at each point shown in Figs. 4-1 and 4-4. First half of upper arm is
chopper, second half is ON, and first half of lower arm is chopper, second half is ON.
Fig. 4-3 Voltage waveform at each point
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 (B) (Fig. 4-5)
(2) When U+ transistor is OFF: (by inductance of motor coil) U coil
→
V coil
→
V transistor
→
Return diode
→
Point (A) (Fig. 4-5)
RAS_25_35_AW_055-086 2003.12.31, 10:59 AM 70