1000W Panasonic microwave oven inverter power factor measurement

Thread Starter

avandalen

Joined Dec 8, 2020
9
I am designing a 1000W Single Stage Battery Charger with Inherent Power Factor Correction. Of course, power factor correction (PFC) is required. To gain knowledge about PFC, I measured the current of a microwave oven with a Panasonic electronic HV supply (Panasonic Z606Y6Y40BP / Y4FFZZ000BP)
Panasonic-Z606Y6Y40BP-Y4FFZZ000BP.jpg
U-I.png
The microwave oven power was set to the maximum of 900W. We see that the input current (i shunt) is far from sinusoidal. Nevertheless, the Panasonic has an EMC approval. Can I assume that a battery charger with a current waveform equal to the Panasonic can meet the EMC standards?
 

crutschow

Joined Mar 14, 2008
25,994
You'd have to measure the PF, not just look at the waveform.
This can be done with one of the inexpensive plug-in power measuring devices, such as the Kill A Watt meter.
 

Ian0

Joined Aug 7, 2020
1,121
Not all EMC regulations apply to high frequency interference. Harmonic currents are EMC, and they can be measured on any digital scope with FFT.
The requirement for a good power factor depends on the type of equipment. Regulations for lighting are the strictest, followed by computers and televisions and then all the other stuff. Microwave ovens and battery chargers can have quite large amounts of odd harmonics. Even harmonics are much more strictly limited.
Crutschow is correct - the first piece of equipment I used for harmonic current testing was a plug-in power-meter with a PF readout. That told me whether I needed to get out the digital scope for a proper measurement.
 

Thread Starter

avandalen

Joined Dec 8, 2020
9
I have found out that a microwave oven falls into IEC 61000-3-2 Class A, with the maximum currents per harmonic in this table:
1.png
To design the EMI filters and the active PFC that are necessary to meet the legal requirements in IEC 61000-3-2, you must accurately measure the current per harmonic precisely., that is not possible with a simple Kill A Watt meter. The Panasonic current (see above) doesn't look like a sine wave and has a lot of harmonics I think. I cannot measure this properly with my Rigol5104 with FFT.
But the question was actually, can someone say from experience that a waveform that looks like the picture above (i shunt) is common in practice and may meet the standard IEC 61000-3-2.
 

Ian0

Joined Aug 7, 2020
1,121
It might, and it might not. Difficult to say with that amount of harmonics.
I’m sure you can measure it with a scope’s FFT, because that’s how I do it. The scope output is probably in dB but that makes the smaller ones easier to see. It’s not difficult to calculate back to amps, using the Kill a Watt reading as the total.
Is your charger >1kW?
is it for professional use?
if so, it‘s exempt.
If it’s less than 1kW (4.3A@ 230V) it would be unusual if it had >2.3A of 3rd harmonic, but harmonics like 7th and 9th are where things tend to fail
 

Thread Starter

avandalen

Joined Dec 8, 2020
9
It might, and it might not. Difficult to say with that amount of harmonics.
I’m sure you can measure it with a scope’s FFT, because that’s how I do it. The scope output is probably in dB but that makes the smaller ones easier to see. It’s not difficult to calculate back to amps, using the Kill a Watt reading as the total.
Is your charger >1kW?
is it for professional use?
if so, it‘s exempt.
If it’s less than 1kW (4.3A@ 230V) it would be unusual if it had >2.3A of 3rd harmonic, but harmonics like 7th and 9th are where things tend to fail
It is a mobile charger for consumers, 1kW, that is IEC 61000-3-2 Class B (if I'm correct)
 

Ian0

Joined Aug 7, 2020
1,121
Let's just recap. What type of power factor correction were you thinking of designing in? I'd say that your microwave doesn't have any.
 

Thread Starter

avandalen

Joined Dec 8, 2020
9
I have done FFT measurements at the Panasonic microwave oven, with the Rigol MSO5104 scope
The microwave oven power is set to the maximum power of 900W.
The output of the ACS712-20 is 10A / V
Current
i.pngI rms = 99mV * 100 = 9,9A
I max = 150mV * 100 = 15A
Measured with a multimeter:
I rms = 9,2A
Pmains = 230V * 9,2A = 2100W
FFT
i-FFT.png
1 n=1 I=58mV*100 = 5,8A
2 n=3 I=21mV*100 = 2,1A < 2,3A (IEC 61000-3-2)
3 n=7 I=5mV *100 = 0,5A < 0,77A (IEC 61000-3-2)
The conclusion is that the harmonic currents meet the regulations.
 

Thread Starter

avandalen

Joined Dec 8, 2020
9
I made a mistake, here is a new FFT image
FFT1.png

2 n=3 150Hz I=2,13A < 2,3A (IEC 61000-3-2)
3 n=5 250Hz I=0,16A < 1,4A (IEC 61000-3-2)
4 n=7 350Hz I=0,45A < 0,77A (IEC 61000-3-2)
5 n=9 450Hz I=0,20A < 0,4A (IEC 61000-3-2)
The conclusion is that the harmonic currents meet the regulations.

Is it correct what I have done?
 

Ian0

Joined Aug 7, 2020
1,121
I made a mistake, here is a new FFT image
View attachment 224698

2 n=3 150Hz I=2,13A < 2,3A (IEC 61000-3-2)
3 n=5 250Hz I=0,16A < 1,4A (IEC 61000-3-2)
4 n=7 350Hz I=0,45A < 0,77A (IEC 61000-3-2)
5 n=9 450Hz I=0,20A < 0,4A (IEC 61000-3-2)
The conclusion is that the harmonic currents meet the regulations.

Is it correct what I have done?
Exactly like I do it!
 
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