# Series Active Filter

Discussion in 'Homework Help' started by Retarded, Mar 19, 2011.

1. ### Retarded Thread Starter New Member

Mar 12, 2011
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can anyone explain to me the mechanism of Series Active Filter?

2. ### t_n_k AAC Fanatic!

Mar 6, 2009
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A secondary switch mode control device which injects dynamically controlled energy in series with AC power feed line(s) to improve overall power quality on the said power feed line(s). The series energy injection is typically accomplished through inductive (transformer) coupling from the switch mode controlled filter into the aforementioned main power feed line(s).

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3. ### Retarded Thread Starter New Member

Mar 12, 2011
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now i have several problems in designing a series active power filter to compensate the harmonics distortion caused by non linear loads

I have draw the circuits using Matlab Simulink, and the circuit are as in attachment!

On the bottom left of my circuits is actually the non linear loads comprising C and R which are use to generate the THD! And on the right side is the active power filter i design to eliminate or reduce the THD! on the top left should be the control circuit i'm using! however the circuits doesn't works!

There are several questions and problems i'm facing as below:

1. Is there anything wrong with the configuration of my entire circuit including the control and series power filter circuit?

2. what value i should use for Lr and Cr (i.e the physical system)can anyone shows me the calculation for both value or what value should be appropriate?

3. i have the circuit with me, can anyone please take the circuit from me and correct any mistake for me? The non linear load circuit currently having 30%THD when it is disconnected with the transformer, after it is connected with the transformer circuit(i.e the series filter) the THD increase to 47%.

4. or anyone can give me a circuit that illustrate how series power filter works.

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4. ### t_n_k AAC Fanatic!

Mar 6, 2009
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There are papers written on the topic but they tend to be short on specifics &/or long on mathematics.

I've seen an implementation of a shunt type of filter (rather than series) in PSIM. In that case the active filter switching control simply seeks to null out the harmonic content of the main power line feed to the non-linear load - such as your rectifier+DC filter load.

One paper I've seen that looks somewhat interesting as background reading is the one shown in the attachment - title/authors only.

This is such a broad and complex topic, you are unlikely to obtain any in-depth support from AAC forums, unless someone with specific experience in this area is willing to "go the distance" with you.

• ###### Paper Title - Active Filter.png
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5. ### Retarded Thread Starter New Member

Mar 12, 2011
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oh i see
so can you tell me where can i approach/get someone with this kinda specified experience?

6. ### t_n_k AAC Fanatic!

Mar 6, 2009
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Don't know. Are you undertaking this as part of a course of studies? If so can you not consult with your supervisor / professor?

There is no control feedback to adjust the compensating inverter stage switching to reduce load harmonic content.
I guess you are simply adjusting the inverter stage and watching what happens to the load THD. It seems that is not helping matters in your case - with the increasing THD. This may not necessarily be the correct approach. I think you would need something fast enough to track harmonics and under feedback control adjust the inverter switching to counteract the harmonic fluctuations.

7. ### Retarded Thread Starter New Member

Mar 12, 2011
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yeah i'm working on my final year project!

8. ### t_n_k AAC Fanatic!

Mar 6, 2009
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I've had a go at a simulation using PSIM - seemed to get a reduction in THD with this layout. Probably nowhere near optimal. Hope it's of some use.

• ###### Active Filter (TNK).pdf
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9. ### Retarded Thread Starter New Member

Mar 12, 2011
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WOW
Thank you so much TNK. I really appreciate what had you done!
However there are certain parts of your circuit i don't understand, can you please explain to me?

1. the non-linear loads you created(parallel C and R then series with L) are randomly create right? and they are connected with a block that is the rectifier right?

2. i see your LC filter comprises of C= micro-farad and L=10mH, how did you come out with these values? can you show me the calculation?

3. i never use the PSIM software before so is your switching bridge equivalent to my inverter block?

4. did you use any PWM swicthing? as i didn't understand the circuit actually!

5. why do you have a 5070Hz and 20Vpp supply while in my circuit doesn't have that voltage source!

6. how did you come out with the 0.0001/5 on the PI block? what are these values? the proportional gain? can you show me how you calculate that?

7. on the load side i see you measuring the voltage and somehow connected with the BP1 block and another which i don't understand as well

8. and how you come out with 1000u value connected to the inverter?

P.S. i'm a beginner in this filed actually so i don't know much about the circuits i would appreciate if you can teach me.

Thanks

10. ### t_n_k AAC Fanatic!

Mar 6, 2009
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I've refined the model somewhat to (hopefully) make it easier to understand.

In reality there is very little calculation involved in the development and I'm not particularly interested in doing the work you should rightly be doing.

As you can see from the annotations a lot of things were just assumed and then adjusted by trial & error. That's where the rigorous mathematical approach should provide an optimal solution.

In any case, this model - however deficient - did give a substantial improvement in the line current harmonic content. Unfortunately I don't use Matlab so I can't help with transcribing the content from PSIM.

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11. ### Retarded Thread Starter New Member

Mar 12, 2011
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Thanks TNK,

your annotation helps, now i understand better