Aurora Inverters I need help!

[Mark Wygant]

This is my first time using this forum. Looking through here I seems like there is a lot of knowledge of the Aurora Inverters. Here is my set up and issue. I have a pair of 5kw VAWT on my house. The are both running the Aurora 7200 Controller/rectifier and 6000 Aurora Wind Inverters. And of course 6000 watt dump loads. The systems are completely separate all the way to the sub panel. When the wind is kicking they don't want to accelerate much over 50 VDC. If I disconnect the AC grid the turbines have no issues running up to 500+ vdc. But as soon as the grid is reconnected it seems the inverter is dragging the turbine back down to 50vdc. I am completely out of ideas. The inverters were programmed by the guys at The Power Store using the power curve from the turbine manufacture. I've all ready fried two of these inverters trying to figure this out and would like to avoid this a second time. I am going to try and post my wiring diagram on here so someone can see how my system is hooked up. Any and all help is welcome.

[Rob Beckers]

Hi Mark,

To start with the "frying" part; These inverters will handle just about any abuse, except for DC overvoltage on their input. If the input voltage exceeds 600V DC the inverter is toast. That corresponds to around 440V 3-phase AC coming from the wind turbine. You absolutely have to make sure the voltage never gets there (or you'll be spending a heck of a lot of money on inverter repairs). That includes the case where the grid power is down, so there is no load on the turbine. Usually this tends to take place during storms, just when the wind is blowing like there's no tomorrow. Nonetheless the voltage into the inverter has to be under control even then.

I've published a wiring diagram that has two possible solutions/scenarios, you can find it at http://www.solacity.com/PowerOneWind.htm, look on the left side with all document downloads for one called "overvoltage protection". Nothing is completely fool-proof, but this is pretty close if it's set up correctly.

To move on to the PVI-WIND-BOX; these switch on the dump load at 540V DC. With many wind turbines this is too late to really keep it under control, regardless of the dump load (a bigger dump load could blow up the alternator, which will keep voltage under control as well, but that's probably not what you're looking for). If you've destroyed two inverters that probably means the dumpload on your turbines is not doing its thing properly; either the voltage where it switches on is too high, or the dumpload too small to have an effect. If you look at the wiring diagram for overvoltage protection mentioned above you'll find one option that can switch a dump load as well as providing overvoltage protection (and you can change the voltage at which it switches on). That could be a better solution in your case than relying on the PVI-WIND-BOX to do this.

By the way, Power-One will 'repair' inverters that were destroyed due to overvoltage. The word 'repair' is in quotes because what they actually do is send you a new one. Of course, it's for a fee (around $1,000), but that's still much cheaper than buying a new inverter.

To get to the part about the turbines not spinning properly when the inverters are grid-connected: The MPPT table in the inverter is clearly incorrect for your turbine. It's putting on too much of a load at low wind speeds, causing the turbine to stall. Normally it's the turbine manufacturer that determines the MPPT table; they either are clueless or scrupulousness and don't care they sell a faulty product. I can help you determine a more fitting table. To do so I'll need to know more about the turbine (picture, so I can see what type of VAWT, exact dimensions of the blades/rotor, the loaded and/or unloaded voltage (AC or DC) of the alternator vs. RPM, design TSR if you have it).

Before you start playing with the MPPT table, you should first put a mechanism in place that prevents the frying of more inverters due to overvoltage though. Changes to the MPPT table invite high voltages (ie. turbines running unloaded or underloaded for some time).

-RoB-

[Mark Wygant]

Thank you Rob for the fast reply. As far as me frying the inverters that was 100% my fault. I was under the assumption that VAWT wouldn't run away and I never installed any kind of dump load. It was a very costly mistake on my part. I now do have dump load that do work (I was playing with them the other night) they kept everything under 500vdc. This is the power curve from the manufacture.

Type***** 6_KW
MPPT Mode****** Voltage
Slope**** 500.000000
Vin******** 50.000000
TProt**** 600
50.000000*********** 0.000000************* 0.000000************* 0.000000************* 1
170.000000********* 782.000000********* 6.516667************* -325.833374******* 1
200.000000********* 1080.000000****** 9.933333************* -906.666687******* 1
228.000000********* 1390.000000****** 11.071428*********** -1134.285645***** 1
256.000000********* 1766.000000****** 13.428572*********** -1671.714355***** 1
270.000000********* 1917.000000****** 10.785714*********** -995.142822******* 1
305.000000********* 2440.000000****** 14.942857*********** -2117.571289***** 1
325.000000********* 2730.000000****** 14.500000*********** -1982.500000***** 1
348.000000********* 3097.000000****** 15.956522*********** -2455.869629***** 1
369.000000********* 3616.000000****** 24.714285*********** -5503.571289***** 1
375.000000********* 3938.000000****** 53.666668*********** -16187.000000** 1
400.000000********* 4440.000000****** 20.080000*********** -3592.000000***** 1
410.000000********* 4756.000000****** 31.600000*********** -8200.000000***** 1
421.000000********* 5094.100098****** 30.736372*********** -7845.912598***** 1
500.000000********* 6000.000000

I dont understand most of this list. THe turbines are from TeckwellPower (Chinese company). The blades are 12.6 feet long tip to tip (straight line,not counting curve) and 13.1 feet across. I don't have much more information on the generators. I hope some of this helps. I will post a picture in a few minutes (I'm on an iPad and it won't let me upload images)

[Mark Wygant]

I also see in these wiring diagrams that there is a wind speed wire hooked up. I had one originally but was then told not to use it because the power curve was loaded and it wasn't needed. Have I been told wrong? Is it still needed. And when looking through the basic menu on the inverters the MTTp is off. I've been told it should be off, just don't under stand why if it is suppose to help improve performance. I really want to learn more about these things but seem to be running out of online sources. Thanks again.

[Mark Wygant]

Here are a few pictures of this project.

[Rob Beckers]

Hi Mark,

You are a brave man, to put two of those monsters on your roof...

The wind speed wire conveys frequency (a measure of turbine RPM) to the inverter. The inverter can work in one of two ways to do MPPT: Either by using frequency, or by using voltage. In your case (as for most wind turbines) it's using voltage, so the wind speed wires are not needed.

I've never looked at the MPPT settings in the inverter, so no answer to that one. The default, as it comes from the factory, is fine. The Power-One Aurora wind inverter are actually just regular solar PV inverters, that run a different firmware. I would not be surprised if some of the menu items came from the PV side, and lost their meaning. For solar PV, the MPPT algorithm is very different, and dynamic (the inverter actively changes the input current to find the best power point for running the solar panels). For wind it's actually much simpler, just a lookup table. For every input voltage there's a corresponding output power level the inverter sets. I have a feeling the 'MPPT enable' setting in the menu is about the solar algorithm, and should be off for wind (again, didn't look into it, just an educated guess).

Looking at the MPPT table for your turbine, it's a bit 'flat'. Power in the wind follows a cube function, your table is quite a ways away from that. The bigger question though is if the power levels are appropriate for the turbine; if they are set too high it would put too much load on the turbine and stall the blades.

Without knowing the exact swept area I can't tell (and I'd need a reference point that links RPM to voltage coming from the alternator). Do you have a link to the spec sheet of the manufacturer? Possibly that has more info.

-RoB-

[Ben Colla]

I'll be up front. I don't have a turbine. This is just a thought.

I'd also want a 2nd fail safe, grid failure, shut down. My thought is to use an electronic actuator (like these http://www.firgelliauto.com.au/ ) powered from mains, holding up a weight heavy enough to brake the turbine. It should be a seperate circuit to the Inverter and it's protection. This way, as soon as there is a grid failure, the actuator fails, the weight drops and the brake kicks in the turbine starts to slow down and stop. Yes, your dump load still has to work and take the full load, but relying on that for an hour while a storm rages with no grid is just asking for problems. This should shut down to a stand still in about 20 seconds.

You'd probably also want a timer to delay powereing up the actuator after grid reconnect. Just in case you get a 10 second grid failure. You'd probably want 30 minutes or so, I think, which should be long enough to allow the storm to pass. You don't want to risk everything in a high wind event. Just shut down and survive.

[Kyori Yoichi]

Hi Mark,

I am not sure but ask Power One whether you need to use one isolation transformer to use two inverters to grid or not.

If you need to use isolation transformer, you need to program one inverter connected to isolation transformer differently. You need additional password which you can obtain from Power One to do this task.

Power one or you may have new 6KW inverter which doesn't require isolation transformer to use multiple 6KW inverters together.

[Mark Wygant]

I've read about the isolation transformers with to two inverters to grid. I wasnt sure if it would be need since they are two separate turbines. I know it is needed when stacking inverters for one turbine. I'm willing to try it but not sure where to get one from. Any ideas? Thanks

[Rob Beckers]

Mark, no, you don't need any isolation transformers. As long as the inverters are not fed from the same source this is not needed. By the way, we sell those transformers, and I've written an article on stacking Power-One inverters (http://www.solacity.com/AuroraStack.htm). Again, not needed in your case, I'm just mentioning it for completeness.

To get back to something else you said, about thinking that VAWTs cannot run away: This is true for the "half oil drum" type, or Savonius to use the official name (and its derivatives). They are drag-type devices that can't speed up much beyond the speed of the wind itself (TRS or tip-speed-ratio, of just about 1 to use the technical term). The other type, the "egg beater", like yours, or Darrieus as it is officially called (and the many variations on that theme) use a real airfoil and those can most definitely run faster than the speed of the wind (ie. their TSR will be much more than 1). They will speed up quickly without a load, and fry the inverter, as you found out.

The previously linked-to overvoltage protection wiring diagram that I wrote will take care of protecting the inverters. It is very reliable if installed properly.

-RoB-