how to calculate the thd of a pfc circuit

Status
Not open for further replies.
H

hanjingyu2008

Newbie level 4
Joined
Apr 19, 2009
Messages
5
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,312
how do you calculate the thd of a pfc circuit ?with filter or without?(Some chips say they can acheive 99% pf, do they include filter or without?)
For a TM/BCM pfc without filter, is 40% thd normal?

thanks
 

you always measure with the filter in place.

......though it may be useful to you to see the thd without the filter first so you can design the right filtration.

PFC's are stinkers for THD..............they cannot be heavily filtered as it would mess up the power factor....but then the high frequencies get into the mains.
 

By definition, THD designates harmonic distortion, which doesn't include PWM frequency components. In so far, it
shouldn't depend strongly on filtering.

According to IEC1000-3, harmonic currents have to measured up to the 40th harmonic at maximum. Even high power
PFC circuits would typically not emit PWM frequencies below 3 kHz. PWM conducted emissions above 150 kHz have
to comply with the respective EMC rules however.
 

If I only calculate the thd from 50Hz to 2kHz,
can the pf still be defined as 1/sqrt(1+thd*thd)?

thank you
 

If reactive power at the fundamental is zero.
 

does anyone know how to plot TDH waveform in Hspice? this might be helpful. THD in terms starting from 60Hz, 120hz, 180....
 

.tran (you time...)
.four freq ov
freq is your base frequency , and ov is the node you want to calculate the thd.
 

I know .tran and .four, but I dont know how to use them for me to see the Current at harmonic frequencies from the .NETLIST file. can you provide me the syntax...? I need 60hz, 120hz,180hz ....... up to the 20th.
 

1.Current THD is calculated by

I thd = √(I²+I³+....+Square of In)/I1

2.TM/BCM Pfc's current THD of 40% is normal without filter.
By proper filter and by the functionality of chips(to tune the inductor current wave shape nearer to zero crossing), even we could bring down to less than 2%
 

1.Current THD is calculated by

I thd = √(I²+I³+....+Square of In)/I1

where did you get this calculation? can you give a reference for this? Thank you
 

maybe all the books about ic design
I know one from "cmos circuit design.layout and simulatiojn"
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…