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Climate Class 6100i / 6000i / 8100i / 8000i
[2] PAM Circuit
1. PAM (Pulse Amplitude Modulation)
The PAM circuit varies the compressor drive voltage. The IGBT shown in the block diagram charges the energy (electromotive force) generated by
the reactor to the electrolytic capacitor for the inverter by turning ON and OFF.
When the IGBT is ON, an electric current ows to the IGBT via the reactor (L1) and diode bridge (DB2). When the IGBT turns OFF, the energy stored
while the IGBT was ON is charged to the voltage capacitor via the diode bridge (DB1). As such, by varying the ON/OFF duty of the IGBT, the output
voltage is varied.
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. Be-
cause 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 “ ” 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 deter-
mined 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 supply voltage.
1) Detailed explanation of PAM drive circuit sequence
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