setting the mppt for a 4.2 wind Aurora inverter

[jarrod9155]

           Could use any advise or ideas here is a proposed mppt table that was provided by Rob at solicity with the iformation I provided to him . The current is what worries him and me . Also I am seeing 8 ohms per leg at the inverter is this to high  this is 12 coils at 19awg 350 turns rotors are 18 inches 16 mags per rotor. Have seen peaks of 2600 watts before furling .I talked with Rob and brought this max watts down to 3500 at about 20 mph winds . Also the blades are gona be 18 foot royalwind blades . I am trying to aim for low wind pruduction 10 to 15 mph my average . Thanks for any help
wind TSR   RPM  Amp  Vac P-alt P-loss  Eff.  Vdc P-out
2     7     49    0   50     0     0    -     60     0
3     7     73  1.1   68   135    32   81%    89    90
3.5   7     85  1.5   76   205    58   78%   100   155
4     7.5  104  1.9   94   304    85   78%   122   250
4.5   7.5  117  2.4  102   416   135   75%   133   360
5     8    139  2.7  122   573   179   76%   158   505
6     8    167  3.9  138   924   365   72%   178   840
7     9    219  4.7  187  1505   526   74%   240  1390
8     9    250  6.0  203  2126   885   71%   260  2000
9    10    313  6.8  264  3127  1135   73%   336  2900
10   10.5  365  8.0  308  4263  1552   73%   389  4000
10.1 11    387  7.8  335  4518  1470   75%   423  4200

[SparWeb]

Your questions deserves a more in-depth answer than I can offer.

It might help me understand if I could do the math on the figures in your data table.  I can compute some power figures from the amps and volts, but they don't all match up.

efficiency = P-output  /  P-input

also:

P-input = (P-output + P-loss)

therefore:

efficiency = P-output  /  (P-output + P-loss)

so

4200/4518=92%

That doesn't sound right, and somehow you get 75%.

Next, 350 turns of 19 gauge wire on an 18 inch rotor is about 360 feet per coil?  For 4 coils per leg of the star then you have 1440 feet.  Multiply by 8 ohms per 100 feet and each leg comes to about 11.5 ohms.  Across the leads you'd get 23 ohms.

Unless you wound the coils two-in-hand, and then there would be 5.8 ohms acrosss the leads.

Do you know the resistance of your stator?


I see the RPM and the TSR still climbing gradually as the wind speed goes up, even at the top end.  This could be a true tracking of the increasing power of the wind.  I guess if I plotted it on a graph, the cubic power curve would become evident.  At what point does the MPPT algorithm adjust the load in high wind to encourage furling?  Can the Aurora clamp the VAC tightly enough to prevent overspeed?  Is there a mechanical furling system on your wind turbine?

Have seen peaks of 2600 watts before furling .I talked with Rob and brought this max watts down to 3500 at about 20 mph winds

Either a typo or I'm not understanding what you mean.

8 Amps running through 19 gauge wire, that doesn't sound too bad. 

You aren't divulging Rob's secret family recipie, are you? 

[jarrod9155]

This turbine does furl at about 28 mph with the old inverter and with 13 foot blades power max . I am upgrading to 18 footer so it should furl alot earlier . And I do have omron voltage sensing relay setup to divert the power to a base board heater to keep things under control . Now for the stator I am seeing 16 ohms per two legs , now this is about 180 feet away over 8 awg stranded copper line so about 8.0 ohms per phase . Now Rob the aurora dealer helping me set the power curve thought this was a little high and figured my stator would go puff at about 20 mph winds just a guess  . I will be trying to get as much as I can out of 10 15 mph winds and on the top end we up the tsr to 10.5 to lower the amps or heat factor witch speed the turbine up . Any ideas on a safe rpm for a 18 foot blade . My generator is built on over kill side structure wise . and is 8 ohms high or average 18 awg 350 turns  12 coils 18 inch rotor 16 magnets per rotor . magnets are 1,2 .5 inches n42.

[Rob Beckers]

Since I'm the one that produced those numbers I better explain: 

The table as published is missing a whole set of (more) numbers, and the efficiency you see in there is strictly that of the alternator, based on resistive losses (and yes, I'm fully aware that ignores many other losses, such as friction and eddy currents). The objective was to keep an eye on those losses and avoid letting out the magic smoke. Maybe that is a non-issue, if the alternator simply won't deliver the power requested by the inverter, I just wanted to be on the safe side. Keep in mind that the MPPT info that I derived is just a 'best effort' based on very, very little information to go on. I don't have a power curve for the alternator, there is no power curve for the turbine, I even don't have a solid number for the unloaded AC voltage per RPM (it's derived somewhat circuitously from a DC number). The calculations also ignore a great many things and assume nice sine waves, good power factors (which is not true for a bridge rectifier) etc. So, the margin of error in all the numbers is large. Lucky for me an MPPT curve can be off by quite a bit without much effect on energy production or behavior of the turbine.

To take the entry for 8 m/s:

I start with the energy in the wind for that wind speed, derated for a reasonable rotor efficiency, which works out to 3011 Watt.

The optimal TSR for these blades and the angle they are mounted at is (I was told) 7. In this case I use a TSR of 9 to get a reasonable alternator efficiency and not generate too much heat in there. So, for a TSR of 9 the rotor RPM at 8 m/s works out to 250 RPM.

At 250 RPM I'm calculating an unloaded AC voltage of 288 Volt (3-phase).

For the rotor to not speed up, nor slow down, the alternator needs to load it up to the same power as the wind is generating, that 3011 Watt, which calculates to a current of 6.0 Amp per phase (that power than splits between losses and what is delivered to the inverter).

The internal resistance of the alternator measured at 16.2 Ohm phase-to-phase, it's a wye configuration, so that's 8.1 Ohm per phase leg. With that, the voltage drop can be calculated and I get a loaded AC voltage of 203 Volt.

With the current and internal resistance the resistive losses in the alternator can be calculated, which works out to 885 Watt.

Now that I have the losses, the available power at the output is the wind input minus losses, which is 2126 Watt. The alternator efficiency is output divided by wind input, or 2126 / 3011 = 71% (this is an approximation, ignoring a few more things).

From the loaded AC voltage the loaded DC voltage follows, coming out at 260 Volt DC.

The power left after losses is taken, together with the inverter efficiency, to generate the power coming out of the inverter, into the grid, which works out to 1980 Watt. That forms the MPPT pair: 260V DC and 1980 Watt.

All the other points are calculated similarly. The reason the TSR increases from its ideal of 7 for the lower wind speeds to 11 at the higher wind speeds is to keep the alternator losses down. As you can see from the table it gets up to 1500 Watt at 10 m/s. That is a lot of heat! My question to Jarrod was if the alternator can handle this without starting to smoke (there's lots of air cooling at that wind speed, but still).

SparWeb, the power in the wind would show a cube curve (though I derate for decreased efficiency at higher wind speeds, where drag increases since the blades are truly whirling around at those RPMs). The MPPT curve shows anything but a cube in this case because the TSR is not kept constant. So, the MPPT curve does attempt to truly track the power in the wind, but it's not a cube. The MPPT curve does not affect furling, that is based on the mechanical/aerodynamic properties of the blades vs. tail, since it is the moment between them that causes furling, and it should furl at just about the same wind speed with or without a load (it better does, since there is no guarantee that the grid is always "on", so there may not be a load at times). The Aurora inverters do not clamp voltage. All the inverter does is present a load, based on the voltage. So, for each DC voltage on its input it will present a resistance of XX Ohm, based on the MPPT curve. This load tops out at the highest point of the MPPT curve, or 4200 Watt in that table, with the actual resistance that the inverter presents decreasing as the RPM/voltage of the alternator increases (higher voltage means higher resistance to keep that load at 4200 Watt).

Hopefully this explains things a bit!

-RoB-

[jarrod9155]

Thanks for explain Rob

[Devo2]

I am on the cusp of buying an inverter & had never heard of these until now, are they pure sine wave & grid tie capable?  I didn't know there was mppt for wind I always just see it with solar beside it.  How big of a power output increase do you notice compared to non mppt inverters?

Devin

[SparWeb]

...Hopefully this explains things a bit!  -RoB-

It certainly does.  Gotta take some time to digest a bit, too.  For instance, I'm not confident that the statement:

...and it should furl at just about the same wind speed with or without a load...

- is entirely true, nor gets to the heart of the matter.  I've got a bit of aerodynamics background, but that's a question that I can still argue either way.  Sometimes I think that a higher rotor speed (unloaded prop) would have more thrust, thus furling is okay, but the counter-argument is that furling is supposed to reduce prop speed, so have we accomplished the goal of protection or not?  Practicalities aside, I would say that furling in 30 mph wind at a rotor speed of 300 RPM is much better than furling still at 30 mph but a rotor speed of 500 RPM.  The critical factor that sets the furl may be the safety of the blades, or it may be the wire ampacity.

Maybe the Aurora's MPPT scheme is able to optimize both, in which case my cheque will arrive in the mail shortly. 

[Rob Beckers]

SparWeb, agreed, furling is different at various RPMs. It's a question of by how much, and honestly, I don't have the answer to that.
My reasoning for that the "furling wind speed shouldn't change much" statement is that the rotor extracts a certain amount of of power from the wind, creating thrust, which is one part of the moment arm together with the tail surface (or some other force), to effect furling.

Even when the rotor is running unloaded, it is still extracting power from the wind, though very inefficiently. Much of it is going towards drag (ie. putting energy into vorticity and such). My aerodynamics knowledge is limited, my background in that realm is in writing code and running atmospheric dynamics models, so I don't know how much it's extracting. Unless it's stalled or furled it will extract energy though, causing thrust. In actuality nobody wants to let their rotor run unloaded (the RPMs and voltages get dangerously high), so if the grid is down it'll likely go to dumpload. That too loads the rotor.

The meat of the matter that I was trying to get at, is that the turbine design should be such that you get it to furl reliably at a low enough wind speed for a variety of loading conditions. It should not rely on the inverter being online, sometimes the grid is down and it won't be.

What the inverter can certainly do is optimize for alternator ampacity so you don't burn it up, and if you have an alternator with enough overcapacity the inverter can be set to put a large load on the rotor for high RPMs (voltages). This could be part of a mechanism to keep the rotor from running away, and may help stall the blades at high wind speeds.

-RoB-

[Boss]

OMG you guys are talking way over my head, still, this is very interesting stuff. I found this by searching MPPT, as I am trying to understand the V/I curve and hope it can help with my setup.
Maybe I have the wrong search criterion (MPPT) and if someone knows of a better search phrase, please let me know. I hunger for knowledge
For instance the last time I read something about MPPT here it seems the algorithms where geared more for PV than axial flux turbines.
Doing a Google search this morning I found a MPPT battery charge controller that stated "Diversion Control Mode: May be used for solar, wind or hydroelectric" this is from the spec sheet of a TriStar TS- 45 
Is it just compatible, or programmable if the user understood these numbers from our turbines?
Need help steering

[imsmooth]

Yo.  I have solved this issue a long time ago for my Aurora 3.6

Reference this page http://www.mindchallenger.com/wind/axial14a.html and I go over the derivation of the equations and I work over some example calculations for the proper data points the power curve.  It has worked perfectly for me. 

My web tutorial at http://www.mindchallenger.com/wind covers so many different topics that I was able to develop thanks to the help of members on this board.

[SparWeb]

Hi Boss,
I just bought + installed a tri-Star so recent experience speaks to your questions.  When I bought my Tristar TS-60 I specifically asked for a non-MPPT from the dealer so that I could use it for my wind power.  Good thing, too, because last week I found in my datalogger records a 35 Amp peak from the turbine that could have fried the old Xantrex controller!

Forgive me if I am stating the obvious but the Tri-Star comes in 3 ratings:  TS-30, TS-45, and TS60   and for each there are two TYPES:  MPPT and non-MPPT.  This distinction may be hidden because they are obviously advertising the newer MPPT product.  I'm pointing it out because the MPPT is not suitable for wind.  The MPPT algorithm is designed only for solar-PV.  And just for the record MPPT = Maximum Power Point Tracking

The reason for this is the means in which the controller switches the current.  In MPPT, the controller is monitoring not just the battery voltage but the PV array's voltage as well.  You program it with some specs from the panel's label (I assume - there could be other ways for the controller to figure out the scheme) so that the controller knows at what voltage the array of cells will be most efficient.  It then regulates the average current to keep the voltage up to that point.

On an array of solar panels, they will have a high open-circuit voltage and a lower voltage where they can produce maximum power in full sun.  Then you hook them up to a battery bank that is probably much lower still, even 24V batts are bulk charging at 28.8V or so, but the panels you have may prefer 32 Volts or more to deliver max power.  A direct, continuous, connection to the batteries will clamp the panel array voltage to the battery voltage and there's no negotiation.  A MPPT charge controller can step in and "pulse" the array on and off.  Now the array voltage goes up to open-circuit V and back down to battery V many times a second, so that the average is around that middle voltage where the PV works most efficiently.  Older controllers can't do that, but the MPPT ones can.  You need to put in more info to program the controller so that it knows what to do.

I see wind MPPT done with inverters, not charge controllers.  This seems to be the preferred method because wind MPPT can use the grid as its load, which is much more responsive than batteries and can absorb virtually infinite amounts of energy, compared to a resistor bank that would have to be run much more often to do the same job.  You can't just open-circuit a wind turbine - or rather, you shouldn't, or better yet, you'd better know what you're doing if you expect it to remain under control!

Rob Beckers, or any other guys who do these setups can correct me, but I think you need to over-size the generator a bit for the prop, too, so that the MPPT control can "tame" the genny at low wind speeds, and "let it loose" in stronger winds to take advantage of both speed ranges.

As usual, there a wikipedia entry on it:  http://en.wikipedia.org/wiki/Maximum_power_point_tracker

[Boss]

Thanks SparWeb
Your explanation seems to have satisfied most of the questions banging against the grey-matter of my head.
I just couldn't get my head around how the MPPT could change the load that is the battery bank which the turbine effectively saw.
Pulsed, aha. Okay, and now I see why it works better for a PV than our wind turbines.
With this straightened out I will go back to the idea of adding a big fat resistor before the battery bank to get our turbine to make 25 amps like it used to before I doubled the bank size.
Then when the brains of our outfit gets back from bikin' around the country and we rebuild the turbine with greater off-set and even longer blades, maybe this experiment will harvest more energy from the wind on top of the hill here in north-eastern New Mexico
Sometimes I wish I was smarter, and could "get" more about what the group gurus are saying, but mostly I'm happy that I "get" as much as I do, and really it is too cool that we, knowing as little about the complexities of DIY wind, are able to get a turbine in the wind last year around this time, and it is still in the wind, hooray!
I hope all the newbies see how this works: Start small, be reasonable, learn as we go, this stuff the brainiacs, say works, we can figure out the details later 
 

[SparWeb]

...Sometimes I wish I was smarter...

Don't we all?

There's only some much any one of us is going to learn from the internet anyway.  Eventually you have to do it build it and try new things yourself.  So on that score we're even (which is the one that really counts when talking about DIY).

[boB]

  A MPPT charge controller can step in and "pulse" the array on and off.  Now the array voltage goes up to open-circuit V and back down to battery V many times a second, so that the average is around that middle voltage where the PV works most efficiently.  Older controllers can't do that, but the MPPT ones can. 

Just a bit of clarification here if I may...
Most of the older so called "PWM" controllers switch the PV array terminals between Voc and  battery voltage many times per second.   MPPT controllers try to keep the PV terminal voltage at the Maximum Power Point Voltage  all the time, except when in battery voltage regulation (i.e. Absorb, Float, EQ)  mode.

boB

[Boss]

...Sometimes I wish I was smarter...

Don't we all?

Absolutely, but one tends to ponder so much with this RE "hobby" that I wonder if I wouldn't be more contented on the couch not pushing my poor old brain to the limit.  Thanks for all the help here

BoB, I love your avatar, awesome, graceful and smooth
 

[scoraigwind]

I'm not confident that the statement:

...and it should furl at just about the same wind speed with or without a load...

Yes I find this very interesting, as I think I am the designer of the alternator, although in my design the wire size is smaller #19 and not #18 and the volts are higher due to a thinner stator. 

There are some presumptions about furling that I find rather worrying.  In my experience, an unloaded rotor will tend to be less good at furling.  So I would expect serious overload if the tip speed ratio is allowed to rise in high winds like that.  It will also be noisy and alarming.  Furthermore I would not use an 18 foot rotor on an eight inch offset like that because that will not furl reliably in the first place.  So you could say I am worried.

You can put an 18 foot rotor on that alternator but I don't understand why, since it is rather too small.  I'd use a much bigger offset (over twelve inches) and be very happy with the low wind performance, but set a low limit on the maximum power so as to have a nice quiet animal in my backyard.

[jarrod9155]

Scoraigwind,
                                   This is your design from the recipe book and it is made of 19 awg 350 turns . I would like to make another stator out of a thicker wire to reduce
the resistance in the stator and still retain the high voltage. As for the 18 foot blades on a machine desigh fo a 14footer it loves it no problems with clearance and it furls at about 20 to 25 mph now . The biggest problem I have had with the machine is it still can be stalled even buy the 18 foot blades . At about 110 rpms i can only pull maybe 50 to 70 watts that a 6 to 8 mph wind .Recintly I opened the pout curve so it lets the rpms get spinning to about 125 before I start trying to pull over 100 watts  anything before that it will fluctuate the watts up and down . I did do the test you specifie, 60 rpms  I should see about 50 to 60 volts ac but this machine does not brake loose of stall till higher voltage. This machine performed its best with a hybrid battery from a prius  hook to it were the voltage was clamped at about 210 volts dc and fruinus solar inverter hook to it during one day I saw 6kw hour . I wonder has any one else reported building this type grid tie mill from your plans . I am still very happy with your plans and thankfull fore the fun and the reliablety it has been .         
                                                            Jarrod, in Maine 

[scoraigwind]

Hi Jarrod,

I based my information on your statement "My generator is built on over kill side structure wise . and is 8 ohms high or average 18 awg 350 turns  12 coils 18 inch rotor 16 magnets per rotor . magnets are 1,2 .5 inches n42" and on the fact that the resistance seemed a bit low for 19 awg wire. 

Also when I looked at Bob's really useful description of his approach I read "At 250 RPM I'm calculating an unloaded AC voltage of 288 Volt (3-phase)." I misread that as DC voltage and thought you had made the stator way too fat and were getting low voltage out.   But in fact it squares with my predictions.  If you do wind one with 18 awg then I suspect it will need a wider air gap and the voltage will suffer, so no gain is likely that way.  I'd make that kind of adjustment for a battery system but in your case i'd make the adjustment in the inverter settings which is a lot easier and just as effective.

I am puzzled that you are suffering from stalling and wondering about changing the winding when you have the magic box that can load the machine at any voltage you like.  I wouldn't have thought it mattered much at all what wire size you use so long as you make a tidy job and fill the available space up with copper - if it stalls then you can just tell the inverter to run faster (less power, more voltage).

Quite a few people use the larger machines for grid tie although mostly with SMA inverters for some reason.  Good protection is very important.  Surges in speed and power are pretty inevitable.  I would focus on energy production in the commonest windspeeds, rather than peak power which contributes less to the overall energy capture but adds a lot to the stresses and risks.

Glad it furls OK for you although I would not have necessarily expected that to work out.  There are a lot of factors in the equation.

cheers

Hugh Piggott

[Dave B]

Jarrod, Hugh and others,

  This is a very interesting and informative thread. Dave Moller and I (Dave B.) are learning much from your contributions here about grid tie and the relationships between the Aurora inverter, Hugh's Axial design and the Royal Gottigen 222 blades. Although we are not as familiar with the grid tie aspect in regards to the inverter program and how it "sees" the load etc. we are very familiar with the blade performance for direct heating loads and battery charging.

  Here are some of our thoughts based on what we know, what we have been reading here and other's comments as well :

  First of all, we find the Gottigen blade profile to be a very good performer in the lower to mid RPM range. It will of course run high speed but the power curve seems to be very strong in the lower to mid tip speeds. This again we have observed for direct heating and battery charging. My 16' blades are set up for cut in at approx. 85 RPM charging 24v 740 AH. They are flying just above stall at this speed pulling about 300 watts in a constant 10 MPH wind. Fully furling about 250-280 RPM. Dave M's 20' is direct heating water and the constant load is tweaked (higher resistance) to allow easier start up and allow more continuos power in the 10-20 MPH range. In a constant 10 MPH wind the blades will continue to fly just above stall pulling about 400 watts @ 80 RPM.

  We are using more poles than your current set up and 1x2x 3/4 magnets. Our gut feeling is and this is just an opinion is that your 18' blades could be much better matched to a different stator or a larger alternator altogether. In your current configuration it seems that because of the higher resistance of the stator (to get the higher voltage needed for your inveter) you are needing to run the machine at a higher RPM to produce reasonable power. Larger wire guage with more room to keep the stator thickness down and yet wind enough turns to get the voltage we feel could greatly increase your output. Shooting for the lower voltage cut in for your inverter with thicker wire would also take advantage of the blade's high torque in the lower RPM. We want to stress that we are not familiar with the Aurora grid tie inverter or the details of programing the load curve but we know that your 18' blades will perform extremely well between 80-250,300 RPM when closely matched to the load.

  As you know and many others here have experienced also is that you can crunch numbers all day long and be convinced that things should work as the numbers indicate. Sometimes this can get you in the ballpark but other times after everything is connected you can be surprised good or bad about what actually happens. Everyone's system is different and that's why we are thankful to have you post your progress. Your blades are different from most here on the board and so adapting them to a "standard" alternator will prove different results. You are paving the way for your own system, many can offer suggestions but very few if any on this board are working with an identical set up. Keep us posted, this is a great learing experience for everyone.

  Thank you,

  Dave B. and Dave M.
www.royalwindandsolar.com

[jarrod9155]

Dave thank for the post my next big change is the stator , I gonna try to fit 17 awg as many turns as possible wild guess would be 300 or so maybe even change the coil structure from round to pie shape to get more wire in there . And to clarify the resistance is 16 ohms between to legs of the three phase  . Any ideas or suggestions would be great on the stator to be .

[scoraigwind]

It's still a surprise to me that the resistance is so low with 350 turns of #19 wire.  I would expect to see nearer to 20 ohms there.  I wonder what shape/size the hole is in the middle of the coils.

Anyway I will state this one more time in case I have not made it clear thus far: it really does not matter what size wire you use so long as you fill the space with wire and make a tidy job of the coils.  I do not believe that changing the number of turns and using a different wire size will improve the situation or avoid stalling or overheating, when you are working with an inverter that offers a wide range of input voltages.  You can do just as much by changing the inverter programming as you can by rewinding the stator.

A coil that has fewer turns of thicker wire will produce a lower voltage.   Take an example:  If the voltage is (say) 20% lower (4/5) then the resistance will be 16/25 time lower which seems good until you figure the current needed to make the same power will be 5/4 times higher, and in the end the losses depend on the resistance times current squared, so the coil will have the same losses for the same power at the same rpm.  So nothing is gained there.

I recommend you play with the inverter settings to avoid stall, and as for avoiding overheating I'd suggest you play safe.  Just furl early.  Don't go for crazy high rpm to get more voltage.  That makes no sense to me at all.   At least that's my advice but you may have different priorities.

have fun

Hugh

[jarrod9155]

A quick update on the axial flux altenator grid tied with the aurora 4.2 inverter. Well the big thing for me has been to optimize the efficincy of the setup , the first setup was with a frunius solar inverter tied in with prius highbrid battery to help with overvoltage and wind speed change the voltage was clamped at 215 with 13 foot blades this setup up put out 6.0kw in a 10 hour period in 15 to 20 mph winds  thats awsome I have yet to get the same power as that day . This weekend I saw good wind average of 10 to 25 mph gusty very turbulant I pruduced 3.875 kw and 3.0 on the next day and today 1.3kw  still no were near 6kw  but better my average over a month 1kw a day not really great at all . I opened up the low end of the power curve or low wind buy reduceing the watts pulled at low end for such it read for 110 volts dc  pull 50 watts and 115 pull 100 watts and at 110 volt dc thats 100 rpms so it very little for 18 foot blades but this has helped my stalling problem with the generator or generator with this inverter. Today watching it spin in a 7 to 10 mph wind I could see the blades spin real fast and I would hear the generator and tower start grouling and the mill would slow right down but not at a mppt rate really to the point it stalls out and has to start back up . I starting to believe at low speeds or voltage the aurora is having a hard  time adding the correct load of resistance to the voltage it is seeing maybe its the generator it self not pruduceing a nice wave form or not having batterys to smooth it out bad rectifier and so on . There is a wind box they sell that has a lot a capacitors in it maybe this is why ? I do know that this inverter is a basic solar inverter with diffrent software for the wind applacation so maybe all it needs is a smoother signal like pv provides  . Another thing this inverter has in programing of the mppt is the pout ramp w/s that is how it reads something to do with how fast it ramps up and down right now it is set at the max 9006.0 w/s not sure what the pruportion means but maybe its to much with a axial flux I was told faster is better buy another proggramer of these inverter but he also is new to the axial flux grid tied .  So if there is any good opions out there I am open to them  . Also note this inverer does not reach full output  power till 178 volts dc