why do we need harmonic reduction in power electronics ?

[desperado1]

I have heard a lot about harmonic reduction in power electronics and the means to reduce it. Why do we need to reduce harmonics in power electronics. What effect does it make ?

 

[dipnirvana]

it has different meaning in different context , for 50hz/60hz harmonics will currupt power signal, hence the distortion of the power quality. There are IEC standard which guide permissible limit of power harmonics.

other is high frequency noise/harmonics above 150kHz which is controled by the CISPR 22 standard .

 

[desperado1]

Thanks for the reply. Everybody says that it will corrupt power signal. How it exactly does...??

 

[eem2am]

your smps draws current in pulsating manner....high frequency pulsation.....this current is drawn through the supply impedance.....and so makes IT pulsate too.

the supply wires with the pulsating current in them also act like an antenna and cause noise.

so oyou try use filter so that the supply current is not pulsating............but is steady and the pulsating current gets drawn from the filter of your psu....NOT from the supplly

 

[analog_match]

eem2am, I think you are talking about power factor correction in the front end so that supply sees resistive load rather than reactive load?

Also won't h.f. harmonics show up in the output thus increasing ripple in the outputif they are not suitable attenuated?

I found a good magazine article that discusses various harmonics in a swithcing power supply system. Hope this helps.

 

[sureshyee104]

hello...any power electronic device is non linear element at first i draw's large amount of reactive power from source it source unable to supply it then input wave get distorted nothing but harmonic in sence it is multiple of fundamental frequncy....in general bridege ckt it self act's as a harmonic source

 

[eem2am]

"eem2am, I think you are talking about power factor correction in the front end so that supply sees resistive load rather than reactive load? "

.. i am talking of filtering the switching frequency harmonics so that they are not drawn from the mains., where they would take up capacity

 

[mess123]

It can be best understood if we consider an example of "running a motor" with harmonics current.
Suppose there is a motor that has rated speed at 50Hz. But if it is subjected to a power source having second or third harmonics like 100Hz/150Hz, then the resulting speed will be different from the one with pure 50Hz supply. The magnitude of the higher order harmonics will actually be less than that of fundamental one.