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Request suggestions/revisions of my personal project plan

Discussion in 'General Electronics Discussion' started by BlackMelon, Feb 22, 2016.

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  1. BlackMelon

    BlackMelon

    188
    5
    Aug 7, 2012
    Hello,

    My intention is to attach a flexible solar panel to an umbrella at a size of this: http://www.beachstore.com/Umbrella_Beach_xl.jpg. I want it to produce maximum 100W output. There will be 3 outlets producing 220Vac 50Hz / 12Vdc/ and 5Vdc . And I want it to operate accordingly to the flow chart pdf file.
    (The battery mode means that load is drawing energy from a battery only. Pure solar mode allows energy obtained from the sun to flow into a load and a battery. Battery+sun mode makes use of energy from both sources to supply a load)

    My question is:
    1. I want to finish this by the end of the upcoming June. Compared to the limited time, is the project beyond my following knowledge and tools?
    - I know how to calculate components of inverters, buck, boost, buck-boost, and flyback converters . Also, I understand the boost's transfer function by reading "Low-Frequency Characterization of Switched dc-dc Converters" proposed by R.D. Middlebrook and his colleagues.
    - I have read some papers about using an inductor and a capacitor to shape current and voltage waveform to achieve zero voltage switching and zero current switching, minimizing switching loss. I guess if I read formulas carefully again, I'll be able to calculate C and L for the job.
    - The part which I know least is making my circuit to be adaptive. Although I've onced learn to tune PID and to make a fuzzy controller, I have never make an adaptive fuzzy-PID control. I don't know either that how much it will allow my circuit to adapt itself to sunglight and also interferences.
    - What I have got in my home are an oscilloscope, a power supply, and a multimeter
    - I have received a bachelor degree in electrical engineering. Power Electronics, and Control System Design are what I'm interested in.
    2. If it's beyond, could you please deduct unnecessary things in your opinion out?


    Thank you
    BlackMelon
     

    Attached Files:

  2. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    How much are you making from scratch? There are lots of devices already on the market tailored to interface Solar Panels and an inverter.
    I see a major problem with 'solar panel' operation mode only though... mainly because the efficient charge controllers use MPPT, which you can't really use with a static load... You should always be running the panels at the highest efficiency you can, and either storing the excess or drawing the excess from the battery pack.
    Have you located the flexible solar panel you wish to use? I found some that will require a 6.5 Diameter Umbrella. So you are not chasing some impossible pipe-dream.
     
  3. BlackMelon

    BlackMelon

    188
    5
    Aug 7, 2012
    I was googling for a static load and a dynamic load. Some said that the former's magnitude is unchanged, while the latter's is subject to do.

    My question is: If I have an R-C circuit, comprising a dc voltage source, resistor and a capacitor as a load. I connect them in series and measure the C's voltage. As the magnitude (voltage) changes over time before going to steady state.
    Can the C be considered as a dynamic load?

    Thank you
    BlackMelon
     
  4. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    I guess in that case C could be dynamic, it's not really what I had meant. You don't have much control over the current draw at any given voltage.
    I should have been more clear in my initial reply. While you are using a battery, you can vary the charge current into the battery to obtain an optimal power draw from the solar panels. If you connect a Capacitor or another device they will simply draw what they need which could result in the output voltage from the solar panel raising higher than expected or dropping lower than expected. The battery provides a very nice buffer for this excess or deficiency from the panel.
    As long as the device you are using between the panel and the device has voltage regulation and a cut-out if the voltage drops too low, you can use it with any device.
     
  5. BlackMelon

    BlackMelon

    188
    5
    Aug 7, 2012
    If I get you right, according to the diagram, why can't we apply MMPT algorithm to the voltage regulator?

    As I know, MMPT monitors and controls the regulator's output current and output voltage, thereby ensuring that the maximum output power is fed to the battery and the load. Am I correct?
     

    Attached Files:

  6. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    You are absolutely right, but without a battery or a dummy load, you would have no-where to sink or source the extra current or voltage.
    The diagram you have would be an ideal setup.
     
  7. BlackMelon

    BlackMelon

    188
    5
    Aug 7, 2012
    So my first problem is to design sensors to sense the problematic case you said. This will allow the panel to be disconnected from the entire grid.
    I'll be working on that. And thanks for pointing out the issue.

    I've seen widespread china solar panels with MMPT converters on Youtube. On the other hand, the technology , in my country, is extremely prevalent among engineers but hardly seen with common people. Have you seen any needs of it in having picnic?

    PS. I think its use would benefit those who own resorts. If they installed such a device, travellers can come to their resorts and plug in his or her laptop to an umbrella while enjoying nature.
     
  8. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    I'm a bit of a tech nerd, and would love to plug my laptop into an umbrella and work under it outside.
     
  9. BlackMelon

    BlackMelon

    188
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    Aug 7, 2012
    That's cool LOL. In my opinion, the main part to overcome the China-made is using a high frequency (smaller device) and adding Zero Voltage/ Zero Current Switching technique to reduce switching loss. Do you think this is a worth trying?
     
    Gryd3 likes this.
  10. Gryd3

    Gryd3

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    Jun 25, 2014
    I'm not in touch with the market close enough to say yes or no, but if it's something you want to try there is little or no reason not to.
     
  11. BlackMelon

    BlackMelon

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    Aug 7, 2012
    What do the words highlighted with yellow in Pg3 and Pg4 mean?

    PS. The page numbers are what a pdf viewer sees, not those printed in the lower-right corner of pages.
     

    Attached Files:

  12. Gryd3

    Gryd3

    4,098
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    Jun 25, 2014
    Higher voltage batteries or battery packs use multiple cells in series. ie, a 12V Lead-Acid battery is actually constructed with 6 smaller 1.2V cells. Unfortunately when they are strung together in series, they tend to charge unevenly... It's like putting 6 springs together... as it ages and wears some cells will charge faster than others and may over-charge or drain quicker. Hobby battery chargers usually have a cell balancer to individually monitor and adjust the charging of each cell to keep them equal.
    I find it amusing that one can claim they can balance a pack of 6 cells with only external circuitry...

    From how I interpret that section. A 'Cycled Battery' is merely a used or discharged battery. Nothing fancy about it.
     
  13. BlackMelon

    BlackMelon

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    Aug 7, 2012
    Thank you for continually answering my questions. At first, I was confusing temperature drift with the one that you've just explained.

    What I'm confusing now is the term charge acceptance. Some sites said if a battery has a charge acceptance of 90%, I'll be able to use its energy only 90%. Does this mean the minimum state-of-charge that it must remain is 10%?


    I've finished reading about VRLA, LA, and deep cycle batteries, and parameters state-of-charge, charge acceptance, voltage drift due to temperature. I'm gonna find more about the lithium ion one. Is there anything else to find more about batteries? If I finish reading this, I'll go ahead to a solar panel and finally the converters.
     
  14. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    haha. some of that is beyond me, but stick around a little longer and see if anyone else jumps in.
     
  15. BlackMelon

    BlackMelon

    188
    5
    Aug 7, 2012
  16. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    Those numbers are typically an 'up-to' value.
    The laptop I own, and many other consumer laptops usually operate in the 60-90W range. I'm sure you can get a laptop to run at 120W but darn... that would be a really toasty laptop. (Most likely gaming orientated)
    You umbrella is going to need to appropriate amount of surface area 'facing' the sun. Luckily, you don't need to double the diameter to double the surface area :)
     
  17. BlackMelon

    BlackMelon

    188
    5
    Aug 7, 2012
    Asking about MMPT again

    As I read Texas Instruments' paper, Introduction to Photovoltaic Systems Maximum Power Point Tracking, it says that the Vpv, which is an output of a solar panel, is changed to meet the "knee" point in the file "Graph.PNG". I used to see these techniques many times. However, can I summarize that the maximum power point tracker in the file "circuit" is adjusting the Rx (the resistance that a cell sees)? What I mean is that if the Rx is too high, a cell is operating at an open circuit condition, thereby blocking current from charging the battery. On the contrary, if the Rx is too low, a cell is working in a short circuit condition, no voltage is gonna lie across the battery. These cases make power = 0W.

    PS. I don't understand the word "result" in page 6 of TI's paper. Could you explain it?

    Thank you
    BlackMelon
     

    Attached Files:

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