18
Input current waveform without PAM
Input current waveform with PAM
Due to the time of no electricity;
• Power factor gets worse.
• Harmonic gets increased.
Input voltage
Energized time is short in
case L inductance is small.
No electricity runs into
diode module because the
voltage at both sides of smoothing
capacitor is higher than input voltage.
Input current
Owing to the increase of energized time;
• Power factor gets better.
• Harmonic gets suppressed.
Release of energy stored in L.
Peak gets down.
Energized time is
extended by
optimization
of L inductance.
Compulsory energizing
by switching.
2-8-2. Outline of main power supply circuit
MUZ-GC, HC, FD25/35, GE
1. At the start of operation
Main power supply circuit is formed when RELAY is turned ON at COMPRESSOR startup.
To prevent rush current from running into the circuit when power supply is turned ON, RESISTOR is placed in sub circuit.
2. At normal operation
When AC runs into P.C. board, its external noise is eliminated in the NOISE FILTER CIRCUIT.
After noise is eliminated from AC, it is rectifi ed to DC by DIODE MODULE 1.
DC voltage, to which AC has been rectifi ed by process , is stabilized by SMOOTHING CAPACITOR and supplied to IPM.
DC voltage, which has been stabilized in process , is converted to three-phase AC by IPM and supplied to COMPRES-
SOR.
3. Purpose of PAM adoption
PAM: Pulse Amplitude Modulation
PAM has been adopted for the effi ciency improvement and the adaptation to IEC harmonic current emission standard.
Outline of simple partial switching method
In conventional inverter models, DIODE MODULE rectifi es AC voltage to DC voltage, SMOOTHING CAPACITOR makes its DC
waveform smooth, and IPM converts its DC voltage to imitate AC voltage again in order to drive the compressor motor.
However, it has been diffi cult to meet IEC harmonic current emission standard by above circuit because harmonic gets gener-
ated in the input current waveform and power factor gets down. The simple partial switching method with PAM, which has been
adopted this time, places and utilizes BOOSTER CHOPPER CIRCUIT before rectifying AC voltage in the general passive-meth-
od converter circuit. As harmonic gets suppressed and the peak of waveform gets lower by adding BOOSTER CHOPPER CIR-
CUIT as mentioned above and by synchronizing the timing of switching with the zero-cross point of waveform, the input current
waveform can be improved and the requirement of IEC harmonic current emission standard can be satisfi ed. Since the switching
is synchronized with the zero cross point, this simple partial switching method has the feature of lower energy loss compared to
active fi lter method. In addition, output and effi ciency is enhanced by combining with vector-controlled inverter in order to boost
the voltage of power supplied to IPM.
4. Intelligent power module
IPM consists of the following components
• IGBT (x6)
: Converts DC waveform to 3-phase AC waveform and outputs it.
• Drive Circuit
: Drives transistors.
• Protection circuit
: Protects transistors from overcurrent.
Since the above components are all integrated in IPM, IPM has a merit to make the control circuit simplify and miniaturize.
5. Elimination of electrical noise
NOISE FILTER CIRCUIT, which is formed by *CMC COILS capacitors placed on P.C. board, eliminates electrical noise of AC
power that is supplied to main power supply circuit. And this circuit prevents the electrical noise generated in the inverter cir-
cuit from leaking out.
*CMC COILS: Common mode choke coils
