Mitsubishi Electronics MXZ-ANA manual Purpose of PAM adoption, Input current waveform without PAM

3. Purpose of PAM adoption

PAM : Pulse Amplitude Modulation

PAM has been adopted for the efficiency improvement and the adaptation to IEC harmonic current emission standard.

Outline of simple partial switching method

In conventional inverter models, diode module rectifies AC voltage to DC voltage, smoothing capacitor makes its DC waveform smooth, and IPM converts its DC voltage to imitated AC voltage again in order to drive the compressor motor.

However, it has been difficult to meet IEC harmonic current emission standard by above circuit because harmonic gets generated 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 the booster chopper circuit (L61, DB65 and TR821) before rectifying AC voltage in the general passive-method converter circuit. As harmonic gets suppressed and the peak of waveform gets lower by adding booster chopper circuit as mentioned above and by synchronizing the timing of one-time 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 satisfied. Since the switching times is just once by synchronizing with the zero cross point, this simple partial switching method has the feature of lower energy loss compared to active filter method. In addition, output and efficiency is enhanced by combining with vector-controlled inverter in order to boost the voltage of power supplied to IPM.

Input current waveform without PAM

Due to the time of no electricity;

·Power factor gets worse.

·Harmonic gets increased.

Input voltage Input current

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 waveform with PAM

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.

4.Intelligent power module

IPM consists of the following components

· IGBT (x6)	: Converts DC waveform to three-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.Smoothing capacitor

C63A, C63B and C63C stabilize the DC voltage and supply it to IPM.

6.Elimination of electrical noise

Noise filter circuit, which is formed by *CMC COILS capacitors placed on the POWER 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 circuit from leaking out.

*CMC COILS; Common mode choke coils

2-7-2. MUZ-A24 MUY-A24

2-7-2-1. Inverter main power supply circuit

POWER BOARD

	NOISE FILTER P. C. BOARD
		R64A/R64B	L
POWER	CT61	X64
SUPPLY
	N/F

PFC

+CB1

CB2

CB3

		V
CT1	U	MC
U		W
IPM
V
CT2
W

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