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Passive Harmonics Filter

ignition_08

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Hi

My design is running on single phase 220V, 50Hz is failing harmonics current emission testing from 5th harmonic onwards. Thinking of using passive high pass filter to eliminate the problem.
Any design application notes or reference filter design to share?

Thanks
 

BigBoss

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Are you sure that you will able to distinguish 200Hz and 250Hz ( 4th and 5th harmonics ) harmonic components by simple passive filtering ? I don't think so.
I believe you have to find more sophisticated solution such as ADC then Digital Filtering.
 

FvM

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I guess you are asking about low-pass rather than high-pass? The filter should pass fundamental and suppress 5th and higher harmonics. That's surely possible but not really practical considering the size of LC components.

Passive harmonic filters have been used in industrial power distribution systems, unfortunately they are very bulky.
 
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ignition_08

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Are you sure that you will able to distinguish 200Hz and 250Hz ( 4th and 5th harmonics ) harmonic components by simple passive filtering ? I don't think so.
I believe you have to find more sophisticated solution such as ADC then Digital Filtering.
The filter need not have such sharp cutoff, reducing 5th harmonics and above will do the job

I guess you are asking about low-pass rather than high-pass? The filter should pass fundamental and suppress 5th and higher harmonics. That's surely possible but not really practical considering the size of LC components.

Passive harmonic filters have been used in industrial power distribution systems, unfortunately they are very bulky.
Yes, suppress 5th and above harmonics will do the job. My input is a single phase 240Vac, 2.3A. Smaller passive components can be used?

What input power level are we talking ?
My device input is a single phase 240Vac, 2.3A.
 

Easy peasy

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you say high pass filter - but surely you want the 50/60 Hz fundamental to get thru .. (?)

I suspect what you really mean is either a low pass filter, or a notch filter centred on 55Hz .... (?)

[or a 5th harmonic trap ... ]
--- Updated ---

assuming the input is a rectifier followed by a 400V cap - then a simple inline copper and steel choke may well attenuate the 5th harmonic enough to pass standards ... - assuming you have room to fit
 

BradtheRad

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A coupled inductor of lesser Henry value can act like a plain inductor of larger value. Add a capacitor and you have a second order low pass filter.

Experiment by adjusting values as desired.

coupled inductor plus cap block freq above 50 Hz 3A.png
 

Easy peasy

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@brad - itwould be interesting to put a cap input filter following a bridge rectifier on the RHS with a suitable load and see the current in the mains .... with and without the 22uF cap

just BTW, 60mH @ 3A peak wil lbe about the size of your fist and ~ 1kg ...
 

ignition_08

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you say high pass filter - but surely you want the 50/60 Hz fundamental to get thru .. (?)

I suspect what you really mean is either a low pass filter, or a notch filter centred on 55Hz .... (?)

[or a 5th harmonic trap ... ]
--- Updated ---

assuming the input is a rectifier followed by a 400V cap - then a simple inline copper and steel choke may well attenuate the 5th harmonic enough to pass standards ... - assuming you have room to fit
yes, you are correct, it should be a low pass filter for my case, suppressing the 5th harmonics onwards
--- Updated ---

A coupled inductor of lesser Henry value can act like a plain inductor of larger value. Add a capacitor and you have a second order low pass filter.

Experiment by adjusting values as desired.

View attachment 177246
--- Updated ---

A coupled inductor of lesser Henry value can act like a plain inductor of larger value. Add a capacitor and you have a second order low pass filter.

Experiment by adjusting values as desired.

View attachment 177246
--- Updated ---

A coupled inductor of lesser Henry value can act like a plain inductor of larger value. Add a capacitor and you have a second order low pass filter.

Experiment by adjusting values as desired.

View attachment 177246
Does it matter if we connect the LPF before (AC input) or after the rectifier?
--- Updated ---

Does it matter if we connect the LPF before (AC input) or after the rectifier?
 
Last edited:

ignition_08

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May i ask, is the calculation of pi filter components same as the LC low pass filter?
Are the same values used for the 2 capacitors in the pi filter?
 

Easy peasy

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you don't want too much capacitance across the mains - as the standing 50Hz current can then get quite high compared to full load current.
--- Updated ---

this is why a single inline L is often used ...
 

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