3.2. 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 wave-
form 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 described above, the ON/OFF operation of the IGBT controls the increase/decrease of the compressor power supply voltage (DC
voltage) to improve the compressor efciency and maintain a high power factor by keeping the current phase closer to that of the sup-
ply voltage.
AC voltage waveform
AC voltage and current waveform when PAM is ON
AC current waveform
IGBT ON period
Zero-cross detection
AC voltage waveform
AC current waveform
AC voltage and current waveforms when PAM is OFF
3.2.1 Detailed explanation of PAM drive circuit sequence
3.2.2 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 (50Hz).
• The zero-cross of the AC voltage is judged as the rising of the clock waveform, as shown in the diagram above.
3.2.3 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.
3.2.4 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
12PHR-N_S530612PHRN.indd 14 2013/8/7 15:42:13
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