How can i design passive filter for unipolar PWM inverter

[ankireddy03]

I am designing 24- 400V DC-DC stage after that I am inverting to 230V ac, 50Hz,
the switching frequency of full bridge inverter section is 50kHz. How can i design LC filter for removing switching haronics to get pure sine wave. can u plase help how to find L and C values.

 

[julioreye]

Re: How can i design passive filter for unipolar PWM inverte

i hope this document be useful for you.

 

[Mr.Cool]

your switching frequency is very high given 50Hz output. ha. since you want a sinusoidal type filter (not dv/dt) set your filter cut-off frequency to be between 600Hz and 5kHz. somewhere in there should be just fine, lots of room to accommodate other design trade offs.

before you can go any further you need to answer more questions

is your system 3-phase?
do you need differential AND common mode filtering?
what power levels?
is your source isolated? how is it grounded, what type topology?
is your load grounded?
what kind of specification are you trying to meet?

pick a value for C and solve for L. your C value will be from standard parts selection. you need a type of capacitor that is suitable for this type of use on AC line as a filter, so pick PTE or film. pick voltage rating to be 600V. what a suitable value for C is depends on how you answer the question above, but it is usually less than 10uF.

Mr.Cool

 

[ankireddy03]

thank you julioreye. how the Q value affect the filter design and how to select Q value.

 

[julioreye]

Re: How can i design passive filter for unipolar PWM inverte

if you want in your system a fast respond you must choose the Q value between 0.5 to 0.7. in the cut off frequency while more Q more increases the magnitude in that frecuency, as result some harmonics couldn't attenuate.

i upload the document for more details. regards.

 

[ankireddy03]

thank you julioreye

 

[qtron]

Re: inductor laminations

your switching frequency is very high given 50Hz output. ha. since you want a sinusoidal type filter (not dv/dt) set your filter cut-off frequency to be between 600Hz and 5kHz. somewhere in there should be just fine, lots of room to accommodate other design trade offs.

before you can go any further you need to answer more questions

is your system 3-phase?
do you need differential AND common mode filtering?
what power levels?
is your source isolated? how is it grounded, what type topology?
is your load grounded?
what kind of specification are you trying to meet?

pick a value for C and solve for L. your C value will be from standard parts selection. you need a type of capacitor that is suitable for this type of use on AC line as a filter, so pick PTE or film. pick voltage rating to be 600V. what a suitable value for C is depends on how you answer the question above, but it is usually less than 10uF.

Mr.Cool

Hello Mr Cool!
I own an LG 1.1 kW VSD - programmable "carrier" frequencies are up to 25 KHz.
I want to build my own output sine filter.
What I REALLY want ot know is, does the laminations of the inductor have to be special, or just ordinary transformer laminations?
I was told, that the harmonic content will overheat the latter. BUT, if that were the case often VSD's are used direct to motors with short cable run. Wouldnt the motor overheat given its laminations are similar to transformers?
If you cannot help maybe others can..
Thankyou,
Qtron