Wind Turbine PWM vs Direct Connect

keyturbocarskeyturbocars Posts: 375Solar Expert ✭✭
I've been thinking about how wind turbines generate power. Currently, I have a HY-2000 2kW wind turbine and it's connected to my 48V battery bank through the controller supplied with the wind turbine. From what I've read, it uses Pulse Width Modulation to charge the battery bank.

I've been thinking about adding another wind turbine to my system. Since I have a Coleman Air 440amp diversion controller, I could add a lot more wind power as long as I increased my dump load. Here comes the question....

If I add another 3 phase wind turbine and just run it through a rectifier and appropriate circuit breakers into my 48V battery bank, would I be losing power with out having a voltage regulator type controller?

Hope this makes sense.

I was thinking about the way that solar panels work and if you hook them up directly to a battery bank and the panel voltage is greater than the battery bank voltage, then the battery bank pulls down the voltage and you essentially loose the extra power that would have been available. Just wondering if this same situation is true of wind turbines. Seems like the potential losses with a wind turbine could be very high because at high wind speeds, the voltages can get much higher than battery bank voltage. Not sure if I am thinking about this correctly though, so that's why I thought I'd run it across some of you more experienced people.

Thanks,

Ed

Comments

  • BB.BB. Posts: 27,788Super Moderators admin
    Re: Wind Turbine PWM vs Direct Connect

    No wind expert am I--but you are correct. If you put a battery on the alternator/rectifier output--the battery "clamps" the voltage to ~12-14.5 volts. And even though the alternator is able to output higher voltage (at higher RPMs) and roughly the same current--that is lost power.

    Using a PWM controller between the wind turbine and the battery bank will not do anything good... A PWM controller just turns on and off very quickly. It does no voltage/current transformation (aka AC Transformer or DC buck/etc. power converter).

    And, anytime you reduce current/electrical load on a HAWT, they run the risk of over-speed (unless you have break/feathering/furling mechanics/etc.).

    So--there is a way you can go with a solar charge controller like solution... That is a MPPT type charge controller designed to work with a wind turbine.

    Basically, the charge controller will figure out the Pmp=Vmp*Imp equation for the alternator at any speed/loading.

    Midnite Solar is very close to releasing their "Classic" MPPT solar charge controller which will have (I don't know the details) a Wind/Water turbine control option. Earlier test results showed that a 2-3x (IIRC) output power increase was possible with wind turbines and MPPT.

    There are/may be other MPPT controllers for off-grid battery systems--I don't follow the field, so I don't have any further information.

    There is lots of other issues that need to be controlled for safety (maximum turbine RPM, fail safes, loading, shutdown, etc.) that I am sure have cause no-end of pleasure for the Midnite engineering team. It will be interesting to see the details when the product is released.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • keyturbocarskeyturbocars Posts: 375Solar Expert ✭✭
    Re: Wind Turbine PWM vs Direct Connect

    Thank you for the information Bill.

    On my current controller, I can watch the Ammeter sweep between 0-60 amps (0W to 3000W peak) during very strong wind gusts. Makes me wonder how the Midnite Solar controller could extract more than the 3000w that I am already seeing. I wonder if the existing controller has some sort of MPPT circuitry already.

    That Midnite Solar MPPT controller sounds very interesting! I plan to try to find out more about it!

    Ed
  • BB.BB. Posts: 27,788Super Moderators admin
    Re: Wind Turbine PWM vs Direct Connect

    Ed,

    Hence the need for limiting conditions... You may not get more energy out of the peak winds/gusts because if the controller is limited to 60 amps (I believe the Classic is larger than that).

    As I would guess (purely a guess, I have never seen one of these guys--controller or people)... For example as the controller approached 60 amps, the controller would actually absorb more current which would cause the turbine to slow down and generate less voltage--Since Power=Voltage*Current, the total power would drop and the turbine will now operate slower because the controller is near its maximum output current.

    For medium speed winds, the controller will attempt to draw less current... The turbine will speed up and increase voltage... At some point, Pmp=Vmp*Imp and the controller will find the optimum peak V*I (higher speed will result in less power, and lower rpm will also result in less power).

    So, the real gain from a MPPT type controller will probably be in the mid range RPMs where the turbine could spin faster (much higher voltage, a bit less current) and generate more power vs just being clamped to battery bank voltage).

    How to limit the RPM and current output of the wind turbine, and what to do with the excess power (battery fully charged, not enough loads--is there an integrated load bank/load bank controller, or do they "crowbar" the wind turbine which brings it to near zero RPM and little power output), are the "details" that they will release when the product is in public hands (again, all guesses on my part).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • keyturbocarskeyturbocars Posts: 375Solar Expert ✭✭
    Re: Wind Turbine PWM vs Direct Connect

    Bill,

    You've got me very interested in the Midnite Solar MPPT Controller. I found some good information on their site.

    http://www.midnitesolar.com/pdfs/ClassicClipper_operation.pdf

    I am very interested in this. I need to contact them and ask a few questions to clarify some things. It would be great to be able to extract more power out of my existing 2kW wind turbine set up. Might be better to invest in optimizing what I have rather than add another wind turbine which adds to complexity and cost.

    Ed
  • BB.BB. Posts: 27,788Super Moderators admin
    Re: Wind Turbine PWM vs Direct Connect

    Thank you Ed... That explains a lot.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • keyturbocarskeyturbocars Posts: 375Solar Expert ✭✭
    Re: Wind Turbine PWM vs Direct Connect

    I've been researching and reading more about the Midnite Solar Classic controller. I e-mailed Robin with some questions and he was quick to reply.

    I am wondering how I can determine the maximum DC ouput voltage of my HY-2000 wind turbine. I want to see if it is below the maximum input 250v rating of the Classic 250. I am trying to determine if I would really need the Clipper (which is a PWM controller and dump load). The current HY-2000 controller already serves these functions. Obviously, if I measure the DC output on my HY-2000 controller, then I will only get the battery bank voltage. Naturally, I can't disconnect the DC output during a strong wind!

    I was wondering if it would be possible to take voltage measurements between 2 legs of the 3 phase wind turbine output and then correlate this to the DC output?

    I can measure across any 2 of the 3 phase legs coming into the HY-2000 controller. Not sure if there is a way to correlate what the rectified DC voltage output would be if measurements are taken on the wild 3 phase AC input.

    Ed
  • keyturbocarskeyturbocars Posts: 375Solar Expert ✭✭
    Re: Wind Turbine PWM vs Direct Connect

    By the way, here's a new video that was just released about the Midnite Solar Classic MPPT controller. Robin from Midnite Solar said his brother made this video. It shows some of the wind programming capabilities.

    http://www.youtube.com/watch?v=IpslcfvrT6c
  • BB.BB. Posts: 27,788Super Moderators admin
    Re: Wind Turbine PWM vs Direct Connect

    Ed,

    From the Operational PDF you found--I believe that the "Clipper" active load between the wind turbine and the charge controller--One of its functions is to limit the maximum output voltage of the turbine so that it will not damage the Classic Charge controller.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • keyturbocarskeyturbocars Posts: 375Solar Expert ✭✭
    Re: Wind Turbine PWM vs Direct Connect

    Hello Bill,

    I was hoping I might not need the Clipper. From what I've seen, it is supposed to cost $1700 and there might be a less expensive version ($850) for AC input only. In either case, it's quite a bit of additional money, and I was hoping I could determine the DC voltage output on my wind turbine to see if it's within safe limits of the Classic. Might be no way to avoid needing the Clipper, but I thought I'd do a little more homework.

    Ed
  • BB.BB. Posts: 27,788Super Moderators admin
    Re: Wind Turbine PWM vs Direct Connect

    I think the Clipper is a requirement if your turbine needs electrical loads for speed control (most HAWT do).

    Obviously the folks at Midnite know their product--So they would be the guys to continue the discussion with.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MisterBMisterB Posts: 156Solar Expert ✭✭✭✭✭
    Re: Wind Turbine PWM vs Direct Connect
    I am wondering how I can determine the maximum DC ouput voltage of my HY-2000 wind turbine. I want to see if it is below the maximum input 250v rating of the Classic 250. I am trying to determine if I would really need the Clipper (which is a PWM controller and dump load). The current HY-2000 controller already serves these functions. Obviously, if I measure the DC output on my HY-2000 controller, then I will only get the battery bank voltage. Naturally, I can't disconnect the DC output during a strong wind!

    I was wondering if it would be possible to take voltage measurements between 2 legs of the 3 phase wind turbine output and then correlate this to the DC output?

    I can measure across any 2 of the 3 phase legs coming into the HY-2000 controller. Not sure if there is a way to correlate what the rectified DC voltage output would be if measurements are taken on the wild 3 phase AC input.

    Ed

    If you put a voltmeter switched to AC between any of the 3 phase connectors and the DC positive or Negative connector on the controller, you will be reading half the AC RMS voltage. Multiply that reading by 2 and divide that number by .707 and you will have the aproximate peak DC voltage. If you have a really good voltmeter, you will get a better reading. Voltmeters are set up for 60hz and read RMS voltage but a really good one will be able to give accurate AC readings for the varying frequency of a 3 phase wind generator.

    Here is a link to a page that gives you the basic circuit diagram for a 3 phase bridge rectifier which is what I used to figure this out and do some kind of DC voltage reading without disconecting the turbine from the batteries.

    http://www.allaboutcircuits.com/vol_3/chpt_3/4.html
  • keyturbocarskeyturbocars Posts: 375Solar Expert ✭✭
    Re: Wind Turbine PWM vs Direct Connect

    You are right Bill. I've been discussing this back and forth with Midnite and they have been very helpful.

    Thank you very much Mister B. That's exactly the sort of information that I was looking for on calculating DC output given 3 phase AC input.
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