AE-X15PU
2 – 8
2.2. High power factor control circuit
This circuit brings the operating current waveform closer to the waveform of commercial power supply voltage to maintain a high power factor.
Because of the capacitor input, when the PAM circuit is OFF, the phase of the current waveform deviates from the voltage waveform as shown below.
To prevent this deviation, a current is supplied during the periods indicated by "O" in the diagram.
To determine the length of period to supply a current, the zero-cross timing of the AC input voltage is input to the microcomputer via the clock circuit.
The power source frequency is also determined at the same time.
The IGBT turns ON after the time length determined by the zero-cross point to supply a current to the IGBT via the reactor.
This brings the current waveform closer to the voltage waveform in phase.
As descr bed above, the ON/OFF operation of the IGBT controls the increase/decrease of the compressor power supply voltage (DC voltage) to
improve the compressor efficiency and maintain a high power factor by keeping the current phase closer to that of the supply voltage.
2.2.1 Detailed explanation of PAM drive circuit sequence
2.2.2 AC clock (zero-cross) judgment
•
The clock circuit determines the time from one rising point of the clock waveform to the next rising point.
The detected clock waveform is used to judge the power source frequency (60Hz).
•
The zero-cross of the AC voltage is judged as the rising of the clock waveform, as shown in the diagram above.
2.2.3 IGBT ON start time (delay time B)
•
Based on the zero-cross of the AC voltage, the IGBT turns ON after a delay time set according to the power source frequency.
2.2.4 IGBT ON time (C)
•
After the above delay time, the IGBT turns ON to supply a current to the reactor.
•
The ON time of the IGBT determines the amount of energy (level of DC voltage rise) supplied to the reactor.
DC voltage level in each operation mode (varies depending on external load conditions)
– Cooling operation --- 220 to 290 V
2.3. PAM protection circuit
To prevent excessive voltage of PAM output from damaging the IPM and electrolytic capacitor as well as the control printed wiring board (PWB), this
circuit monitors the PAM output voltage and turns off the PAM control signal and PAM drive immediately when an abnormal voltage output is gener-
ated. At the same time, it shuts off the compressor operation.
The protection voltage level is as follows.
60
about 9 mS
7
C8
C9
– Heating operation --- 260 to 290 V
0.004
1.7ms
1300uS
