IVT AE-X12GR-N Service Manual page 16

AEX12GRN
When the IGBT is ON, an electric current flows to the IGBT via the reactor (L5), (L6) and diode bridge (DB2).
When the IGBT turns OFF, the energy stored while the IGBT was ON is charged to the voltage doubler capacitor via the diode bridge (DB1).
As such, by varying the ON/OFF duty of the IGBT, the output voltage is varied.
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 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 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 efficiency and maintain a high power factor by keeping the current phase closer to that of the supply voltage.
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
AC voltage waveform
Clock
IGBT ON
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 240 V
– Heating operation --- 220 to 280 V
Reactor
Stored energy
L5
L6
IGBT ON
IGBT OFF
A
B C
2 – 12
DB1
DB2
IGBT
AC voltage waveform
AC current waveform
Zero-cross detection
IGBT ON period
AC voltage and current waveform when PAM is ON
A
B
C 0.25 2.3mS
50Hz
1.2mS
1.2mS