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Combined buck & boost converter?

Discussion in 'Power Electronics' started by flippineck, Mar 18, 2018.

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  1. flippineck


    Sep 8, 2013
    I gave up trying to use a car alternator as a wind turbine generator, and simply bought a purpose-made PMA generator as a base for my wind power project.

    Some idea of the characteristics of the generator (some figures manufacturer-given, others interpolated & guesstimated, I imagine also the actual blades I end up using would affect the figures to a greater or lesser degree):

    wind   (mph)    rpm   V    A        W
    0      (0)
    1      (<4)
    2      (4-7)    10    1    0.1      0.1
    3      (8-12)   32    3    0.36     1.08
    4      (13-18)  75    6    0.75     4.5
    5      (19-24)  150   12   1.5      18
    6      (25-31)  300   25   4        100
    7      (32-38)  500   43   7        301
    8      (39-46)  750   60   10       600
    9      (47-54)  1000  70   11       770
    10     (55+)    elec / mech damage if unsecured.
    11              braking reqd above 1000rpm / 70V

    The output of the generator is via one positive stud terminal, and the aluminium case as the negative line.

    The SLA bank I'm using is four 12V 110Ah deep-cycle leisure batteries in parallel.

    Thinking about a control setup, I thought I might need the following features:

    - I have many days of very light winds so often, a voltage boost might be useful (even though it might only deliver the lowest of trickle charge)

    - despite that, I do get plenty of very gusty weather so a buck function to keep the charging voltage down to something good for the 12V SLA battery bank would be useful (rather than a simple regulation by just 'throwing away' anything above say 13.8V)

    - some function to either dump through a heater, or simply switch off, the charge current once the SLA bank is full

    - some function to keep a lid on the charge rate of the SLA bank under the windiest conditions

    - some function to apply a brake to the rotor hub at generated voltages above say 70V to try and avoid bearing etc. damage in storms. Maybe just a control voltage to actuate a mechanical brake or something

    Problem is, I've searched far and wide on Ebay and I can find all these features, but never all together in one unit capable of handling sufficient power. None of the individual solutions I've come across seem readily interfaceable with each other so I guess I'm going to have to try home-brewing something, unless I can find a supplier of a perfectly matching all-in-one controller

    I have allsorts of ideas running through my head involving high power relays, zener diodes, buck/boost converters and water heating elements

    If anyone has any ideas, suggestions, links to suitable products etc I'd be interested & very grateful to hear.
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    The circuit you're looking for is called buck-boost converter or sepic converter. You'll find them readily on internet sales platforms for different voltage and power ratings.
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Like with solar panels, an mppt controller is the best solution for getting maximum power from your turbine.

    Dynamic braking in high winds can be done in several ways. Most simply a dead short can be placed across the output of it is too windy. Other options include feathering the blades, or having a blade geometry which stalls in high wind conditions.

    Placing what is essentially a very high power zener diode across the rectified output may help, but in very high winds the power dissipation may be enormous.
  4. Bluejets


    Oct 5, 2014
    Alternator regulators do not "throw anything away" as you put it. They provide the necessary excitation to give a desired output with reference to requirements.
  5. flippineck


    Sep 8, 2013
    Thanks folks.. might be a silly question to some but, any suggestions for good places to look for suitable buck-boost converters? I'm only really familiar with Ebay & have spent quite some time rooting around there.

    I did see some self-stalling blades but assumed it was no more than a marketing ploy. Will look again at that one as it seemed a neat solution if valid!
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