# Circuit diagram of an active power filter

1. Nov 28, 2012

### slog

Hi
Is anybody in the house that can help with circuit diagram of an active power filter for mitigating harmonic current.

2. Nov 28, 2012

### yungman

A little context will help. Freq, current, voltage etc.

3. Nov 28, 2012

### slog

Last edited by a moderator: Nov 30, 2012
4. Nov 29, 2012

### Staff: Mentor

Describe your needs, the origin of the harmonics, and whatever else is relevant. Is this a homework exercise?

5. Nov 30, 2012

### jim hardy

simplest one i ever saw was a series tuned LC for 180 hz (3rd harmonic of 60HZ) to clean up inverter output..

6. Nov 30, 2012

### slog

@all tanks so much. I ve a research i'm working on, it's all about a induction furnaces in a steel company inducing harmonic current back to the line. I am trying to develop an active filter to mitigate the harmonic current in the line. so i'm in need of active power filter circuit diagram that will help to reduce such effect on the line.

7. Nov 30, 2012

Do a search on ieee.org, google scholar or similar with the keywords active filer, induction furnace, harmonics and you will see that this topic of research has been well discussed. Many different topologies and control strategies have been proposed. For detailed discussion on basic inverter/filer topologies you may need to consult a book on power electronics.

Research builds often/mostly/every time on previously work. If you don't know of these papers you may waste your time re-inventing the wheel.

8. Dec 1, 2012

The answer will also depend on the type of induction furnace - if it is a line frequency furnace - filtering may be the only option and active filter is advised as the current harmonics change with load and material types. For a higher frequency furnace you are typically rectifying the line and then making the output current with IGBTs or other system - here it may be better to look into an active rectifier.
In ether case the challenge is not so much the power electronics circuit - but developing controls that will work reliably - so this not something that I would advise as a one off solution.
To properly apply ether / any solution I would advise a power study - typically done by connecting a Power Quality Analyzer to the system for a few weeks to evaluate the range of harmonics and possibly PF issues - a solution can then be sized around that data. The biggest problems I have seen in large scale filtering ( Static, Switched and Active) is a lack of up front analysis - leading to oversize or slow responding systems - that then cause system wide disturbances.

9. Dec 10, 2012

### slog

@Windadct, please do you know any theoretical method i can use to calculate the harmonic current instead of using power quality analyser as ealier suggested. the following are the specification of the furnace: 1． Equipment type：KGPS600-0.8
2． Rated input voltage: 380V；
3． frequency of input current:50/60HZ；
4． 3相；phases of input power: 3 phases
Rated input current:960A(270mm2 copper cable recommended )
5． Rated output power 600KW
6． Rated output frequency 0.8KHZ±20%；
7． Rated output voltage : 1500V
8． Output phase: 1 phase
9． Rated capacity : 1 metric ton
10． melting time: 1.0MT/Hout
11． Cooling water consumption:18TON / Hour
12． electricity power supply(recommend): 600KVA
Thanks.

10. Dec 14, 2012

Hello Slog..... Sorry for the delay, there is really no way to predict this, you need to know a lot more about the design of the device as well as about the power system it is connected to. The chap way to build these is with just a rectifier front end with minimal to no built in filtering- here in the US you would not be able to use this - 600KW/960A with no filtering - Ill bet you have over 100-200A harmonic current - really a mess.

At this power level - I really can not comprehend trying to do this on the cheap.

11. Jan 9, 2013

### slog

@windact, thanks alot. i appreciate you. The problem with my research is just that the company i intend to use are not allowing me into company. i need to obtain subsequent harmonic currents and voltages from the above fundamental current and voltage, can you please out. thanks

12. Jan 9, 2013

If a supplier can not / will not say how bad the harmonics are - look for another supplier - the active filter that can accommodate this will cost more than buying a better system to start with.

13. Jan 9, 2013