A 2kw prototype system without batteries

[Edgar Paternina]

Hello Everyone,

I am a retired electrical engineer living in a farm 6 years ago, in Colombia. South America, with average winds of 6.3m/s and next week I will be installing the system in the attachment. I really would appreciate any comment from you experts in this field. As you can see I will use a Kipor Inverter Generator with pure sine wave, to start the Aurora inverter when the grid is off, as normally we have outages just when trees go over the power lines because of the high winds, an ideal moment for wind generation.

Thank you in advance

Edgar

[Rob Beckers]

Welcome at Green Power Talk Edgar!

6.3 m/s annual average wind speed is pretty windy! You're a lucky guy. Just make sure that the wind turbine you are using can handle high winds. At those winds the good and bad get separated rather quickly.

The diagram looks good as far as the on-grid part goes (I'll get to the off-grid part in a moment). We use Aurora inverters as well with the 6kW Scirocco, and you can find the wiring diagram on our Web site (http://www.solacity.com/Docs/Scirocco%20Hookup.pdf). Has the manufacturer tested this turbine with an Aurora inverter? They work very well, but have a few requirements that have to be met: The DC input can never, ever exceed 600V, or you'll have an expensive paperweight on your hands (not covered by warranty either, the inverter logs the event in internal memory before dying). I assume the controller has a rectifier build into it? The inverter needs DC while most wind turbines deliver 3-phase AC down the tower. The input has to float with respect to ground, so no grounding of the negative lead or the alternator. Finally, you need an MPPT table for the inverter. Does the installer or manufacturer have one? Or are you supposed to make your own? If you need help let me know, I've been making quite a few MPPT tables for various wind turbines lately.

Now, how well you will fare with keeping the inverter online while the generator is running is hard to say without trying it. The main problem will be to keep the generator within the frequency window of the inverter. The Aurora only stays online within 59.38 ... 60.42 Hz. This is largely a UL1741 requirement (though Power-One has actually set the boundaries a bit narrower than required). If your generator is one of the newer ones that use an internal inverter you should be OK. If it has a mechanical governor you may have a problem, I don't think those are able to keep within such narrow limits. Especially as it will see very rapid and large load changes (the wind picks up and within a second the Aurora is supplying a few kW, so the getset will drop that same few kW in load, and this keeps going on and on rapidly since wind is never constant). The voltage window of the inverter should be OK; it will stay online within 90% - 108% of nominal, and you can change the nominal voltage in the setup if needed. The diversion load will have to be fast enough to ramp up the load if the voltage increases, so the inverter doesn't get over 108%. One inherent problem that I can see with this setup is that the genset is going to see energy flow in both ways (unless that diversion controller can keep the voltage within a very narrow window). The genset is in essence a voltage source, the Aurora is a current source, when the wind picks up and the Aurora's voltage rises to push power onto the grid it'll start backfeeding the generator with any excess beyond the local loads. The generator will have to deal with this excess power.

Hope this helps!
Please let us know how things work out if you are going ahead.

-RoB-

[Edgar Paternina]

Dear Rob,

Thank you so much for your extensive help!

Well for the first question about the manufacturer testing their generator with the Aurora inverter, they say they did, and the controller has a Vmin_MPPT = 100DCV and Vmax_MPPT = 400DVC, so I hope it will ever, never exceed the 600DCV, but body knows until the experience. For grounding I will install three independent and connected copper earthing and take them to the corresponding ground of the controller and inverter and so on, and most probably an arrester too.

Oh yes, the problem with the MPPT curves, was the real challenge as it was very difficult to obtain that curve from chineese manufacturers, I failed business with a first one because of that curve. But with one I did, I obtained that DCV voltage range above and I had to develop a sotfware for obtaining the whole curve so that Magnetek engineers could program the inverter. See attachment. The books by Hugh Piggott were a great help. Anyway I really would appreciate any comment and help from you in this respect, thank you!

About the frequency problem, when the grid is on I hope that the controller will give the correct voltage to the inverter and then it will give the correct frequency, when the grid is on.

Another problem is with the Kipor IG1000 when the grid is off! I really don't have any idea how it will work but I hope it will! This is my main risk.

In a long conversation with a Power One engineer, I saw the main problem was precisely both to maintain the voltage within normal limits a reason why we have the HuangYa Dump load controller; and I suppose that the pure sine wave promised for the generator will give the correct frequency, see:

http://www.kipor.com/pro3.asp?type_id=260

The current generated from generator will be purified by inverter and will be performed a transform from AC to DC, then to AC. As a result, the voltage output will be indendent of engine speed and voltage aberration will be no more than 0.5% and sine wave is smooth

So these new Inverter Generators seem to use the same technique as WTGs, and I really hope they will! As a matter of fact, these Kipor guys seem to give a good service on line, and they declare somewhere their company is based in Taoism principles.

Yes, Rob, my main idea is to share this experience with you through this excellent Forum!

My best regards

Edgar

[Rob Beckers]

Hi Edgar,

The 'grounding' part I mentioned was to say that the turbine and DC side has to float (ie. not reference ground), because the Aurora inverter needs this. As to grounding and lightning protection; I've written a number of pages that try to capture the essence of it, you can read it on my Web site (http://www.solacity.com/Lightning.htm).

Are you getting the inverter with the MPPT curve already programmed? If not, let me know and I'll send you the information for the software that you need to download to do it yourself, named AuroraInstaller (http://www.solacity.com/Docs/AuroraInstaller%20Manual.pdf), it's not difficult but requires some understanding of what's what. The MPPT curve that you show is a bit odd, in that it follows the usual pattern up to 2kW, and then gets very shallow. Usually these curves track up ever steeper to whatever maximum load you want to allow on the alternator (in theory it's a cube function, but real wind turbines and alternators are not quite that efficient, so in practice it's between a square and a cube function. With the MPPT curve you have the turbine is going to be spinning very fast in that region between 2 and 3 kW.

Your generator has an inverter build into it, so yes, I would think it has a very stable output in terms of frequency and voltage. Definitely has a good chance of working OK with the Aurora!

-RoB-

[Edgar Paternina]

Hi Rob,

Again thank you, but I think I have understood you about floating in the sense that both the turbine and controller must not be connected to ground; as ground is obtained independently by copper rods, i.e., a third independent cable for the ground, is this ok? Both the controller and inverter has this ground-point that are quite independent of other electrical point-connections, I think this is what you mean by floating, is this ok?

Yes, the inverter is already programed with Vmin-MPPT= 100 and Vmax-MPPT= 400, I hope, because you are right as between 2kw and 3kw that curve sent by YUENIAO seems not to be ok. In fact with my software the theoretical curve is quite different, see the attachment, so I really would appreciate your help here as I have already taken a look to your pdf, Aurorainstaller, but where can I download it? How must I connect the Aurora inverter to the PC? In the corresponding CD sent with the Aurora inverter there is no information about this.

I took for granted that up to 2kw, it was ok, but to 3kw, the furling system made the curve quite different, but I think after reading your recommendation I must reprogram the inverte again. From that software, Aurorainstaller, it seems to be easy, but it's a real challenge for me!

As the Kipor generator has an inverter included now I am more optimistic it will work.

My best regards

Edgar

[Edgar Paternina]

Hi Rob and Everyone readind along,

Well this time I just want to update the system I will install this week with real pictures, and following some recommendations regarding grounding and lighting protection, both from Rob and Hugh Piggott. Regarding the power vs DCV curve, fortunately the Aurora inverter can be reprogrammed as many times as we need to obtain the best curve for the system. So I hope I will correct very soon the error found by Rob in my theoretical curve.

My best regards

Edgar

[Rob Beckers]

Hi Edgar,

Looking good! :clap2:

I would be interested in what Hugh had to say about lightning protection. Affordable protection that actually works is still hard to come by (I can supply nearly foolproof lightning protection, but it'll cost $2K and up, making it not worthwhile for small wind turbines).

-RoB-

[Edgar Paternina]

Hi Edgar,

Looking good! :clap2:

I would be interested in what Hugh had to say about lightning protection. Affordable protection that actually works is still hard to come by (I can supply nearly foolproof lightning protection, but it'll cost $2K and up, making it not worthwhile for small wind turbines).

-RoB-

Hi Rob,

Hugh says that lightning is not a big issue in Scotland but basically recommended to use copper rods interconnected both for the tower and inverter. I really will take the risk to do just that as this what I have done here in my place with no problem yet. As soon as I have new experiences with my installation I will be sharing it with you!

Best regards

Edgar