What is sweep?

unyalliunyalli Solar Expert Posts: 120 ✭✭
I have an SS-MPPT and no idea what sweep is. There is a Sweep_out, Sweep_Vmp, Sweep_Pmax and Sweep_Voc. I understand Vmp is Volts at max power and Voc is Volts open circuit but what is sweep?

By the way, I did a search in this forum on sweep and selected the first result and searched that page for the word sweep and it was not found.

Jeff

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What is sweep?

    Basically it's sampling the power from the panels to find the Maximum Power Point. Some do it periodically, some do it "continuously". The various addenda refer to what it's checking for and/or basing its power point on.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: What is sweep?
    unyalli wrote: »
    I have an SS-MPPT and no idea what sweep is. There is a Sweep_out, Sweep_Vmp, Sweep_Pmax and Sweep_Voc. I understand Vmp is Volts at max power and Voc is Volts open circuit but what is sweep?

    By the way, I did a search in this forum on sweep and selected the first result and searched that page for the word sweep and it was not found.

    Jeff

    Try using Google search instead of the built-in search in the Forum.
    So your search string would be "site:www.wind-sun.com sweep"

    I did that and got nothing but relevant threads, and even the right page within the thread.
    SMA SB 3000, old BP panels.
  • unyalliunyalli Solar Expert Posts: 120 ✭✭
    Re: What is sweep?

    Ok did the google search with much better results. Still no idea what the heck sweep is.

    Some quotes:

    the MX-60 is a sweep and sleep unit, most of the time, it will be stable and only vary when its sweeping the array. Sweeping the array??? Huh?

    The MX60 will generally hold its array voltage between periodic sweeps. However, during a sweep, the array voltage will vary widely as it typically sweeps between 90% and 50% of the array Voc. Double Huh???

    Is there a doc somewhere that explains sweep in the SS-MPPT?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What is sweep?

    Read my post. I did explain it.
  • unyalliunyalli Solar Expert Posts: 120 ✭✭
    Re: What is sweep?
    Read my post. I did explain it.

    Sorry, your posts confuse me more than the others. Thanks for answering but continuously send me on wild goose chases is down right un frendly. You havin' a bad day? Here are some of your posts.

    How often does an MPPT controller sweep? Depends on the controller. The old MX60's you were left without a doubt as it says "sweeping" when it's doing it. Newer controllers continuously re-evaluate their parameters. Does this mean the newer continuous MPPT controllers like the SS-MPPT don't sweep? (what ever sweep is).

    On the up side, the MidNite Classic will probably handle this better than an old Outback MX60 as I think the Classic doesn't do "sweeps" but rather readjusts continuously. I don't recall if the FM80 sweeps or is continuous. Again with the sweep vs continuous.

    The sweep MPPT stops every so often and sorts through the input available power and output load needs and re-determines the maximum power point. The continual type keeps reconfiguring all the time without the need for the periodic recalibration sweeps. Again we state the newer continuous MPPT controllers don't sweep (what ever sweep is).

    If the Morningstar SS-MPPT-15L does not sweep why are there sweep variables?

    Whats means more to me, array power or Sweep_Pmax?
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: What is sweep?

    In general it means that it periodically varies the effective load ("sweeps" from a high to a low value or vice versa) that it presents to the array searching for the point of maximum power delivery.
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: What is sweep?

    I don't think anyone is being unfriendly.

    Try this and see if it helps,

    http://en.wikipedia.org/wiki/Maximum_power_point_tracking

    Tony
  • BB.BB. Super Moderators, Administrators Posts: 32,026 admin
    Re: What is sweep?

    I give it a wack... A MPPT charge controller starts at zero amps (which is Voc for the solar panel/array) and starts adding current (load into the battery bank) until the the Varray drops to roughly 60-50% of Voc-array (all over the period of a few seconds +/-).

    The controller then takes that data and multiplies Varray*Iarray for every value of I measured/logged. It then looks for the highest power (V*I=Power) and uses that Varray=Vmp for the next 5-15 minutes. The controller will now modulate the current from the array to keep Varray=Vmp-for that X minutes. Then after X minutes, the controller will do another Current/Voltage "Sweep" looking for a new Vmp-array.

    Note that the Vmp-array and Imp-array is (mostly) the result of temperature (Vmp is very affected by temperature, Imp not too much). The the MPPT controller is really just finding Vmp @ temperature for those conditions (sun, wind, angle, etc.).

    The charge controller itself is (usually) a "buck mode" down converter. That can efficiently (around 95% efficiency) take the power from the array (higher voltage, lower current) and down convert it to lower voltage / higher current for the battery bank. It is sort of like an automatic transmission optimizing the RPM of the motor to the Speed of the vehicle.

    The "sweep" is just finding that optimum array voltage point for the MPPT controller to hold while driving current to the battery bank--Kind of like finding out which gear ratio is best for the conditions when driving a car.

    It is, "graphing" the Voltage*Current curve for the solar array and finding the peak of that "search/sweep".

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: What is sweep?
    BB. wrote: »
    Note that the Vmp-array and Imp-array is (mostly) the result of temperature (Vmp is very affected by temperature, Imp not too much). The the MPPT controller is really just finding Vmp @ temperature for those conditions (sun, wind, angle, etc.).

    The Imp value may be grossly different over time, since it is directly proportional to the amount of sunlight hitting the panels. But the Vmp value at which the current reaches its maximum will be dependent on temperature and on the panel string's cell chemistry and design. Unless there is partial shading involved, it will usually be close enough to a constant fraction of that exact string's Voc that some so-called MPPT controllers just use that constant multiplier instead of sweeping at all. (Courtesy of the wikipedia article.)
    SMA SB 3000, old BP panels.
  • BB.BB. Super Moderators, Administrators Posts: 32,026 admin
    Re: What is sweep?

    Thank you Inetdog,

    Yes, my sentence got a little sloppy there. The current is pretty much a function of light energy hitting the panel, and Vmp is pretty much a function of temperature.

    After all is said and done, the Vmp-array will be around 80-90% of Voc.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • unyalliunyalli Solar Expert Posts: 120 ✭✭
    Re: What is sweep?

    Ok I believe I have it now. A "sweep" is varying the load from 0 amps to the amount where power is greatest. As amps pulled from the array increases voltage drops and amps*volts continues to increase to a point where it no longer increases. This is the maximum power point. This is a sweep.

    ALL MPPT controllers "sweep". Some do it faster and more often than others. Some controllers take a few seconds to do this some do it in a quarter of a second. Some do it every 10-15 minutes some do it more often.

    Thanks all, Jeff
  • BB.BB. Super Moderators, Administrators Posts: 32,026 admin
    Re: What is sweep?

    Yep, that is it...

    Some older MPPT controllers just take, for example, 85% of Voc and call it a day. Sometimes, a sweep occures when clouds pass over, etc., and the controller locks onto the wrong Vmp point until the next sweep, etc. And, this is my guess how the basic process works. The details are sometimes patented when somebody figures out a new/better way to do it.

    We are so used to voltage sources (batteries, utility power, etc.) where the voltage is, more or less fixed, regardless of load, that we hardly ever think or have any experience with a "Current Source"--Which solar panels are.

    Turns out that to get the maximum power from a current source (real life current source where the V*I=P does not have a fixed peak), that this is what has to be done to find the best voltage operating point.

    There are some very interesting properties to current sources that make for some very interesting uses in electronics. I will give you one to think about--An "ideal" battery has very close to zero resistance. But an "ideal" current source has very close to infinite resistance. Think about that--An energy source with infinite resistance--how can it work?

    One way to figure out resistance is:

    Ohms = Voltage / Current

    Another is:

    Ohms = change in voltage / change in current

    A battery has very little change in voltage from zero to its maximum output current.... So you get near Zero/current range which is very nearly zero Ohms.

    A current source, would output a fixed current, and the voltage source will change a great amount (i.e., 20 volts/0 amps, 19v/1a, 18v/2a, 17v/3, 0v/4a). The ideal current source has a fixed current or a change of current near zero, and anything divided by near zero is near infinity.

    The common items we work with that are current sources are Arc Welders and Ballasts for Florescent Lights/LED Lights, etc... Where we want a fixed current vs a wide variation in load voltage.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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