Connect grid tied solar inverter to DC+ Bus of VFD?

In summary: I have been thinking about that for a long time, but I have never had the courage to try it.There are numerous commercial solutions meant to tie homes with rooftop solar to the grid. They integrate the inverter and auxiliary functions into the same box and call it "interface". Homeowners typically buy or rent the interface from the power company.But I don't know of any similar commercial packages to interface AC generators to the grid. That is probably because AC generators come in all sizes from kW to GW.
  • #71
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Connect grid tied solar inverter to DC+ Bus of VFD?


Just throwing this out for comment.

What about feeding two VFD's in series. The first one fed with a reasonable "abundance" of fused amps at rated full 480AC volts from the generator. First VFD would be programmed to control max current that the "grid tied solar inverter" can handle (which I guess is what Baluncore suggested in the last post). And then direct those first VFD output lines into the input of a second identical VFD, and then trying to do something with the DC+ voltage of the second inverter for any impedance mismatching?

The first VFD would be a good current limiter; but maybe just a good fault controller/detector for over current. Probably just a dumb idea but just throwing it out there. Maybe just another non starter idea. I'll look more into the Baluncore possibility of "programming a VFD to generate a constant output current, then rectify that for input to the "grid tie converter".
The Allen Bradley VFD's I'm looking at boast Common DC+ buses which can handle regeneration from other VFD motors etc. I'm not worried about losing 2% to 3% efficiency losses with each stage. Right now I'm wasting 100% of potential useful electricity.

.This reply made was apparently made
Man, do you have more inverters than you can use? Everyone in a inverter drag a few motors, you are 2 inverters drag a motor. You can try the inverter more, will burn the inverter, inverter output is not able to have current input. And ac series received if two phase opposite it becomes no voltage, is no electricity, if wave folding wave voltage double, your motor will be crazy, then smoking is small, inverter will fry it's difficult to say. END of REPLY

My response would be ...The only "load" was to be the "grid tie inverter". No motors would certainly have been a part of such an experiment.
However; for those interested...I will post an actual working solution which should/will impress any electrical engineer. It would be worth everyone's while to actually read that solution which is probably posted immediately below.

I do thanks those who actually did submit several suggestions that (trust me) were deeply appreciated... and without their help; I and one other person would not have come up with this solution that all other did not bring forth. Thanks to those persons.
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  • #72
This actually does work flawlessly with an Aurora PVI-6000-OUTD-US-W (Wind Inverter which is now a Legacy Product; but this setup would in all likelihood work equally well at least with the Currently available ABBwind inverter line up too 120KW or so). Not to confuse anyone...but ABB "grid tie SOLAR inverters" could quite probably be turned into "Voltage Source" wind inverters" by using the Voltsys Voltage Control Units (cost 450 Pounds plus shipping of another 23 pounds). They are European Certified but not yet in US or Canada (I believe). I say that because CSA certified manufacturers od "Wind grid tie Inverters" are all include in a very short list at the present time. Not so for "solar"...thus that lead for those interested.

However this solution below uses a CSA certified "Grid tied Wind Inverter" and without any modification of any kind of the "wind grid tie inverter" (ABB/PowerOne/PVI-6000-)UTD-US-W
except user permitted MPPT Curve changes and your choice of available AC output voltages to the grid; and any 6 rectifier (the unit which experimental user can figure out its acceptance for any certification requirements; fusing protection etc.) .....a person can DO THE FOLLOWING

It seems that instead of a wind turbine generating syynchronous 3 phase AC "wild" varying voltages and frequencies depending on wind speed; can be replaced by a different power generator such as a natural gas driven commercial gen set producing synchronous 3 phase AC power (with certeainly even gh current to supply a 600 watt "Wind grid tie inverter.

As in case of the wind turbine; the genset first has to have that 3 phase ACpower rectified to DC for input to the "Wind Grid Tie inverter"; and once the inverter has done its initialization to check for grid presence; generator presence and all parameters including checking for ground faults are within ranges...its as simple as throwing an AC Connect switch and a Grid connect/disconnect switch (which you have obviouslyalready done at your own peril of making some mistake.) Of course after the electrical application and electrical inspections and approvals. Had to say that for benefit of only certain people.

Now some would say why so many transformers; in my experimental setup. Experimental setup is 3 phase 480v ac gen set...transformer to step down to 208 V 3phase...feed this power to 3 phase 208 to 6 pulse rectifier (certainly less ripple produced in 340 DV volts out than any single phase rectifier)...connect to Aurora PVI6000 wind inverter MPPT (parallel) observing polarity and less than 600V DC at all times ...Let inverter do its thing and ...connect synthesized AC inverter output with power factor near 1 to a...single phase 240/208 step down transformer (provides ground fault isolation plus correct 208 single phase to inject into grid). Note grid transformer is 120/208 3 phase and "wind output" is injected into one leg.
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  • #73
Nice! And thanks for the progress report.
Of course in an actual oil field setup you would want the multiple inverters to feed different phases of the grid, or use 3-phase inverters.

Any idea yet on what the payback period is for this configuration?
For a large installation would a micro-grid be practical, where you completely supply your local load and grid-connect only as needed? (Power company may not like that and charge extra.)
  • #74
Tom: As you know...bright ideas; and unique application of old ideas on the invention side are one thing; whilst being permitted to implement that technology can present its own insurmountable issues.

Such may not now be the case in this instance; because in the last 3 months the utility has revised the "NetMetering" program for generation capacity of less than 100KW DC. There is a 61 cent per watt subsidy (That is reckoned to be about 20% of project cost). Off the top of my head; $315 application fees; electrical permit and fees based on fair market vales of work and material; gensets etc etc and buying three Aurora wind inverters (if they can be found ) the 61 cent per watt refund based on generation capacity (no transformer changes should be required; payment to utility for extra electrical meter and some expending some unexpected costs will no doubt be incurred...I WOULD EXPECT THAT I"VE JUST MADE SOME EXTRA MONEY; and covered all extra costs above the already installed generator and BEFORE even generating any power.

I know there won't be any further cheques; but now the small power producer can bank any excess electrical production into the grid as credits; and they would accuulate good for usage for a fixed three year term. The benefit to me would be I would only run the generation for a fraction of the year and (and until the Utility might be convinced that it would be better for everone to generate into grid on a 24/7/365 basis) I would use credits to allow shutting down the genset when my electrical demand is low. Just to save putting unnecessary hours of use on equipment.

And not to mention an abundance of useful waste heat; a backup power sys for any electrical failure (grid or my generation side.). And as i read the application this applies in the province to "Net Metering" of wind, solar, biomass, flare gas, all on the same terms.
To actually sell power is limited to much bigger projects in the million to tens of millions of investments. That one is probably a non starter for only but the bigger oil companies. On that front; in the last month the Provincial gov't has enacted regulations for a 5 year phase in of methane reduction (by oil field producers) of an estimated 4.5 million tonnes methane (reduction of 40-45% of 2015 levels) . There's 16 pages of legalize regulations I just printed off , haven't had any time to read it all but I see that it may only apply to "Business associates" (Licensee of an oil facility)" who emits more than 50,00 tonnes of CO2 per year. Then there are associated royalty credits ad investment credit of 15-25% to offset...and red tape and penalties etc all spelled out. Got to study all that tonight.

The micro-grid isn't probably in the cards; other than supply whatever your business and yourself wish to hook up on "your" side of "their" electrical meter. But that sounds pretty good to me . Not perfect but a whole lot better than 3 month's ago
  • #75
Good luck.
looking said:
I know there won't be any further cheques; but now the small power producer can bank any excess electrical production into the grid as credits; and they would accuulate good for usage for a fixed three year term.

I hope you realize that is a valuable gift to the producer. Those credits have the functionality of a multi-year battery with the costs being paid entirely by other people. It can only result in higher power costs for everyone else in the Province. However, it would be extraordinarily difficult to accurately account for those costs. But it is trivially easy to calculate what it would cost for the producer to buy the equivalent with his own batteries.
  • #76
I totally agree about both the actual subsidy of 61 cents a well as the "multi year battery" statement and I guess it comes with a "full replacement warranty". But this isn't the only example of distorting what would be done if left to your own resources; as opposed to putting the horse power behind making something fly that isn't even aerodynamically shaped to do so.

What about the concept of a 61 cent subsidy for something like solar that can only operate about 15% of it nameplate/boilerplate output capability (on a yearly basis). At least flare gas AC synchronous generation has the capability of being a "base load "energy supplier. That's a six fold advantage in infrastructure usage (to electrical consumers). However there's apparently nothing stopping just generating enough to cover personal monthly or 3 year grid usage.

I do hope that readers are not seeing that this use of "waste" fossil fuel energy; is counterproductive to any crusade to altogether do away with any conventional oil related hydrocarbon usage. That absolute phase out date had better be very carefully determined.

If there is any general support for eliminating subsidies (across the board)...put me on the list of last ones to receive their entitlements.
  • #77
Looking: If you so choose, it sounds like you have the beginnings of a new business venture installing these things.

Eagerly awaiting your next "But it can't be done" project.
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  • #78
Tom.G said:
Looking: If you so choose, it sounds like you have the beginnings of a new business venture installing these things.

Eagerly awaiting your next "But it can't be done" project.
Time for 3 year update to an approved "Carbon neutral" grid tied CSA approved and power company approved Net Metering connection
Some said it couldn't be done.
So tell it to the Chief electrical inspector, Intertec and The provincial power utility and Department of Mineral Resouces and even the Federal government.

Think power bills of two digit size with zero electrical charges; not one cent of carbon taxes and use of tens of thousands of kwh's of banked net metering production. That two digit dollar charge is for the base electrical meter.
If any are still interested in Selected Aurora solar inverters changed to identical wind inverter versions; or potential DC voltage transmission to distant grid tied sites fed from a central synchronous flare gas generating site then speak up. I've learned some things that are not now arguable by persons in charge of approval processes .Unless some nearby neighbor comes up with an extension cord; the remainder of unused banked KWH's to the tune of 40000 some kwh's will be reset to zero later this year. And it could be significantly more but for the fact that the natural gas gensets and "wind inverters" were not run most of this winter because their waste heat not being needed for building heating requirements. Not to mention the additional kwh's that would be donated back.
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  • #79
Hi looking,

I've read your post about feeding excess generated AC back to the grid using a solar grid tie inverter. I found it very interesting and similiar to what I am planning to do myself.

Our irrigation ponds overflow during the winter causing soil erosion, so we installed a 160mm pipe all the way down to the river (800m long, 70m drop) to divert excess water back to the river. This is a perfect site for hydro power, with which we have experimented using an old pump as turbine. We have multiple spare grid tie inverters, ranging from 8- 20kw. We plan on coupling an old single phase alternator to the pump/turbine, rectifying that AC to DC, then feed that DC to a 3 phase grid tie inverter to reduce our utility bills.

After hours of research, you were the only one who seemed to have achieved it at this scale. I was hoping you could give me some pointers on who to "clean" the dirty DC, so that the inverters would accept it, without significant power losses. I know it can be done using capacitors and dump & discharge resistors, but is that enough to smooth the ripple? Also, how does adding a VFD help in this regard? Do you increase the frequency prior to rectification to help smooth the ripple?

Let me know your thoughts on this. Any pointers will be much appreciated!
  • #80

@looking has not been seen here in over a year. In his post #27 he discovered that the usable approach was to use an interface designed for wind powered generators.

Those windmills generate 3-phase AC at wildly different voltages and currents depending on wind speed. There are also commercial grid-tie controllers to connect those to the grid.

I suggest you read thru the thread to gather the extremely useful and detailed information of his endeavor for your project.

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