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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.
+
V
Upper arm
transistor
Lower arm
transistor
Upper arm transistor is controlled to ON/OFF by 2.5kHz-5kHz 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. 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.
+
U
V V
Voltage at
A
280V-300V
Upper arm transistor
Current at
B
When power is supplied U + → V - , 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. 3-3)
(2) When U + transistor is OFF: (by inductance of motor coil) U coil → V coil → V - transistor →
U - 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)
+
W W
W
-
-
V
V
U
T
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
E
F
+
+
U
V
-
W
-
transistor ON
U
T
– 43 –
Time
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