Simultaneous AC/DC power transmission in domestic wiring

Discussion in 'The Projects Forum' started by Darshika, Jan 10, 2015.

  1. Darshika

    Thread Starter New Member

    Jan 10, 2015
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    Hi,

    I am starting to work on project related to the above topic. However all the sources I have so far found are in the area of high voltage.

    Can anyone suggest me any useful resources?

    Thanks in advance
     
  2. crutschow

    Expert

    Mar 14, 2008
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    That's not a common technique.
    What's the purpose?
     
  3. Darshika

    Thread Starter New Member

    Jan 10, 2015
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    We are researching on implementation of DC networks in developing countries. Solid state transformers are being used currently. And I need a solution to tap the solid state transformer at multiple places and take out AC and DC flows.
    Essentially this is similar to filtering out base and treble notes in audio systems.

    Hope the purpose is clear. Thanks
     
  4. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    Seems overly complex for simple residential power distribution. What advantage would a system have?
     
  5. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Won't the DC component play havoc (e.g. core saturation effects) with attached loads, such as normal transformers and AC motors, which are expecting to receive AC?
     
  6. crutschow

    Expert

    Mar 14, 2008
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    Why DC networks?
     
  7. MaxHeadRoom

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    Jul 18, 2013
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  8. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Pulling the AC power out of a modern DC/DC power supply won't serve much of a point or purpose being that it is a very high frequency PWM power that is highly dependant on what the internal feedback loop of the DC/DC conversion process is inside the solid state transformer as you call it.

    What I am saying is that internal AC is not the normal 50 - 60 HZ at a normal AC line voltage thats usable by common devices and appliances. What it is is pretty useless for anything but what purpose it serve inside the unit.
     
  9. Darshika

    Thread Starter New Member

    Jan 10, 2015
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    Sorry for the delay in clarification.

    The idea is this. If power generated through a PV panel is fed to the typical system, the DC power will be converted to AC and transmitted to the appliances and at the appliance AC will be converted back to DC. The requirement is to avoid the conversions by transmitting the DC power itself using the AC network. At the sink, there should be a solution to filter out the DC power from the feed.
    We are required to use 230V ac to transmit a maximum of 48V dc.
    The purpose of the entire solution is to avoid the use of inverters for ac-dc conversion.

    Thanks
     
  10. #12

    Expert

    Nov 30, 2010
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    If you're going to try to separate 50 Hz or 60 Hz AC from DC, you are going to need huge, oil filled capacitors at each AC device. It's cheaper and more reliable to add a separate wiring system for DC.
     
  11. Darshika

    Thread Starter New Member

    Jan 10, 2015
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  12. Darshika

    Thread Starter New Member

    Jan 10, 2015
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    http://www.google.com/patents/US4916734
    above patent specifies a method to separate ac and dc in subscriber line circuits without using RC circuits. If the same concept can be implemented using power electronics wouldn't it be viable?
     
  13. MrAl

    Well-Known Member

    Jun 17, 2014
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    Hi,

    It sounds like you are talking power electronics, not some rinky dink signal that has to be detected. There is a world of difference.
    To detect signals there are different ways, but to get power there are a lot of problems that have to be solved and some issues that have to be addressed.

    First, to put DC and AC together on one line with one common means the AC will be riding on a DC offset. The DC offset has to be removed to get the AC back and the AC has to be removed to get the DC back. There's power involved so it requires high power components.

    But there are other issues that will come up too which throws a wrench into the whole idea. What DC voltage do these so called appliances operate at? They wont be all the same will they? That will mean more than one level of DC will have to be sent and that is just impossible without allowing switch mode power circuits which it sounds like you want to avoid.
    Also, everyone that is already on the grid now will have to be notified in advance that they will be required to install the proper equipment in order to deal with the new power service.

    So it is probably best to do it one way or the other. If you transmit DC then each consumer can convert theirs to AC when needed, but then you again have the problem of what DC level to send cause you only get one choice. AC is better because it allows simple conversion to other voltage levels with a transformer, and if there is a problem with efficiency in the rectifier circuits then perhaps see if you can upgrade those circuits instead. Synchronous rectification is becoming more wide spread now with the push to conserve energy.
     
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  14. alfacliff

    Well-Known Member

    Dec 13, 2013
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    the simplest would be to use ac, and have a dc supply plugged in at each home.
     
  15. #12

    Expert

    Nov 30, 2010
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    Sure. Right after you find an op-amp that can output several kilowatts while being powered by a wire that has both AC and DC currents available in it.
     
    Last edited: Jan 12, 2015
  16. alfacliff

    Well-Known Member

    Dec 13, 2013
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    there should be a way using two center tapped transformers, but I forgot where the diagrams are. dc out the centertap, ac balanced to zero on centertap, ac out secondary of transformer. would require specialized trransformers, and the dc would add or subtract fromj the peak ac voltage, as well as posability of maagnetic saturation of transformer cores.
     
  17. tcmtech

    Well-Known Member

    Nov 4, 2013
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    I see near zero practical application for trying to distribute low voltage DC power over normal voltage AC lines simultaneously being the actual electrical line circuitry and its limitations would make it virtually impossible to be of any real use give the cost that would be involved.

    First off the whole concept would be limited in it power transfer capability by what ever the size of the wire is and its length the 230 VAC system is made out of which means that putting 48 VDC on a small wire intended for 230 VAC power is not going not transfer any major amount of additional power through the system.
    For example, say a circuit has s a 10 map fuse limit. At 230 VAC it could carry up to 2300 watts but at 48 volts it would only carry 480 before the fuse blows. No gain there. Next given the line resistance drops loosing 10 volts off of a 230 VAC power line going any reasonable distance is no big deal. loosing 10 volts off of a 48 volt system going the same distance all while carrying only 1/5th the power is a big deal.

    Second with the AC power sending power backwards through system and the main power transformer to any other part of the system is easy and not a problem.
    Putting 48VDC on the same line basicly short circuits itself when the DC power gets to the first transformer rendering the whole concept pointless.

    Third, common practicality wise there are very few devices and appliances that are mass marketed that use a 48VDC power. Most items that use DC power are lower voltage and lower power plus are easily powered off common AC/DC power packs. Theres no point in sending a odd DC voltage through the system that would require special power packs to convert the DC into another DC voltage when power packs for converting the 230 VAC to whatever DC voltage is needed is already done by cheap mass produced items.

    If you want to feed DC power of any voltage back onto a AC power system that is already easily done with cheap mass produced grid tie inverters which allow for wide range DC input power to be converted into usable stable 230 VAC power that can be distributed to any device that is on the AC system cheaply and efficiently.
     
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