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

[looking]

Just be aware the 1.41 thing is for rectification only, if the VFD or inverter is actually running and commanding negative torque for positive rotation (ie generating), then the DC bus (output) voltage cannot be determined from the AC line voltage of the connected machine.

Got ya.

 

[looking]

Got ya.

Just want to check how the DC bus responds to motors on "quick starts" as well as "ramping" up to programmed speed over a more extended time.

 

[jim hardy]

:"Keystone Carbon" is another source of inrush current limiters...

 

[looking]

This is my note to Ametherm

I'm seriously investigating and developing an electrical device using "US and Canadian standards approved " off shelf AC synchronous 3ph gensets ( eg Kohler ntural gas drive 30 to 60 KVA gensets) with the AC output connected to a DC converter (eg. 3 ph Variable Frequency drive like an Allen Bradley 22B-B033N104/A VFD)
I require "inrush current control" to use the DC+ common bus of the VFD to a "grid tied wind inverter" (s) (Such as Allen Bradley Aurora PVI6000-OUTD-US-W)

The reason for such an arrangement is to develop equipment that an electrical inspector would approve for a "grid tie inverter" in as simple a manner as the electrical utility would allow for wind or solar inverters.

The conventional synchronous control mechanisms are onerous when it comes to relatively small scale synchronous AC production; and my extensive web searches as well as posts to an active thread "Physics forums" (under thread "Connect Grid Tied "wind" inverter to DC+ Bus of a VFD?") has provided encouragement that there are of several commercial solutions to "grid tie" problem solved for solar and wind small scale producers... THAT COULD BE readily adapted to small scale synchronous production of power; and then "grid tied" using standards approved "grid tied inverters".
Could you please send me a free sample of two M35-DIN sufficient to provide the DC "inrush current " control for the setup described above. If successful I will certainly be a "paying" customer next time!
I believe this will be a relatively unique solution that so far eludes such small power producers (utilizing a "casing or "flare" gas which is presently more commonly vented or burned and commonly now has a reputation of a product that oil companies would actually give away to get rid of it)

 

[jim hardy]

Could you please send me a free sample of two M35-DIN sufficient to provide the DC "inrush current " control for the setup described above. If successful I will certainly be a "paying" customer next time!

You're asking him to research that device.
You really ought to do that yourself and tell him what is input characteristic of the load and what is output characteristic of source.
IOW
What is short circuit current available from source
What is input impedance of the load (how many microfarads, how much resistance and inductance in series with it)

because he has to size his thermistor to heat up in your desired timeframe with whatever current you tell him will flow through it.

Those things only cost a few bucks and he can't afford to invest a week in your prototype.

 

[looking]

ABB is off the list:
Quote I am sad to report that ABB exited the Wind inverter business several years ago. We have nothing to replace the items you were inquiring about.

Good Luck UnQUOTE>

Maybe they could be a lot more forthcoming in their current web presence. Sure they list their "Legacy" products including the "Trio" line; but absolutely no where does anyone say "Not available" or "dicontinued".

And as you can see they apparently have nothing to offer other than really big stuff. Does that go for solar too?

Not being an electrical engineer...I'd say so. If you believe a web search there is probably absolutely nothing different in hardware between a solar inverter and a wind one. Its absolutely (maybe) all in the MPPT curves. In fact its damn interesting to read what Voltsys (European solution) is offering for a "Voltage Inverter Control Unit" . First glance says that all ABB Legacy wind and solar inverters can output sine wave AC.

There are apparently even manufacturers who have gotten to the stage of manufacturing combined wind/solar inverters that will allow hardwiring in both energy sources at the same time.

Go figure

But I just found an ABB offering of a 50 or 60 kW version of a PV inverter.

Its on the edge of being too big; but I will investigate. If they have got it figured out how to input synchronous AC--- rectified ---DC bus ----ABB 50-60KW ABB inverter (assuming other comment gleaned from the web are true) then all that would stand in the way is sticker shock

 

[looking]

Product manual is here

https://library.e.abb.com/public/fac0e77e6c3f4bdd953de640bcef1411/TRIO-TM-60.0-US-480-Product%20manual%20EN-Rev%20A(M000041AG).pdf

Web says its a new item and ABB brags about a 10 year warranty. Shouldn't be obsolete yet (I would think)

 

[looking]

Voltsys Inverter Control UnitFor turbine manufacturers with their own rectifier / dump load and turbine control, the Voltsys Power Control unit allows any wind or hydro turbine to work with the wide range of ABB solar inverters.

Wind and most hydro turbines need power extracted at different rates, depending on the RPM or turbine voltage. This is known as a power curve, or power table, and usually the ratio is non-linear as per the example graph on the left. In the past, wind inverters provided the ability to enter a power curve.

The Voltsys Inverter Control Unit provides power curve control for ABB solar inverters, including the Trio and Uno DM range of inverters.

This means that solar inverters can now be used as wind inverters. The load on the generator is increased based on a generator speed or DC voltage and that power is then exported to the grid by the inverter.

The control unit also provides data logging to a micro-SD card. Programming the power curve and other settings is done by loading a setup file on the micro-SD card and a USB port allows for monitoring turbine performance on a laptop.

Manual

Please find a product manual by clicking HERE

If required the usb drivers can be downloaded HERE

 

[looking]

Another page from voltsys.com

Wind Turbine ControllerAre you looking to purchase a wind turbine controller? If the answer to that question is yes, you should visit the Voltsys website today. Established back in 2008, the business has been designing control systems and providing inverter solutions for small wind turbines, providing clients with high-quality products for the most excellent prices in the industry. We use remote desktop to provide online support to customers worldwide, including UK, Mainland Europe, USA, Korea, Australia and New Zealand.

Here at Voltsys, we have worked closely with ABB and have modified our controllers so they override the MPPT tracking in solar inverters. Our controller stores the wind turbine power curve and manages the inverter. Using this system, we continue to supply controllers and inverters for small wind and micro-hydro systems. Our controllers enable you to have fully functional wind and hydro inverters using the ABB solar product range from 1.2kw up to 120kw, these systems can also be used in off-grid applications.

We have a truly excellent reputation for our tech support and our expertise in system design as an establishment, something we hold great pride in upholding with each of the clients we work with. If you require bespoke controller design, we can even provide consultancy and one-off design depending on your requirements. We want to ensure each of the clients we work with are 100% happy with the services we have provided, so you know we are the very best company to work with.

If you are interested in purchasing a wind turbine controller, you need to visit the Voltsys website today. Give us a call on 0151 324 5588 to have a chat with a member of our excellent customer service team. Alternatively, fill in the contact form on our website with all your relevant information and someone will get back to you as soon as possible.

 

[Tom.G]

That could be just what you are looking for. Their manual looks nicely detailed for the installer.

(Of course as an engineering geek, I would like to see the 200pg service manual. Although I'm not sure I would find the time to read it.)

 

[looking]

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


looking

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.

 

[looking]

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.

HERE IT COMES AND IS SUMMARIZED as follows
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.

 

[Tom.G]

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.)

 

[looking]

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

 

[anorlunda]

Good luck.

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.

 

[looking]

I totally agree about both the actual subsidy of 61 cents a watt...as 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.

 

[Tom.G]

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.

 

[looking]

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.

 

[Dassie]

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 similar 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!

 

[Tom.G]

@looking has not been seen here in over a year. In his post #27 https://www.physicsforums.com/posts/6131692 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.

Cheers,
Tom

 

[steelauzzy]

I have access to a large number of flare gas sites, I also have access to a large fleet of generators of various sizes. The large units are easy to sync but the small ones not so much. I’ve been thinking of trying a similar test for a while and just stumbled on this forum.

I’m interested to see this proven out and implemented. Last year I successfully lobbied to allow own use and back feeding to be permitted on any scale. Now I gotta take advantage of it!

 

[steelauzzy]

I have access to tons of flare gas sites and generators. I was going to test this idea when I stumbled on this forum. Does anyone have any photos or data of this setup in action?

 

[looking]

I have access to tons of flare gas sites and generators. I was going to test this idea when I stumbled on this forum. Does anyone have any photos or data of this setup in action?

Hey fellas:
I'm actually still alive and just ran across "steelaussy"'s recent post.
For those interested in flare gas or waterpower or even small scale wind net metering; here are my observations.
IT WORKS ...AND IT CAN produce a significant surplus of unused power (that can and does get confiscated at the end of the contract term period) In my case last October 2023 that amount was in excess of 20000kwh's. On top of that, the year of the contract involved continuouslyusing a 15kw electrical heater and aeration fans to decrease the amount of "piggy banked" electrical credits.
In the current contract period there is already >58000kwh's banked despite adding a Ford Lightning and a Chev WT electric vehicle charging to the net metering system.
I'm going to post this an add a bit more below.

 

[Dassie]

It is much easier than it sounds.

We tried the wind turbine approach with capacitors, rectifiers and solar grid tied inverters. It works well with good energy yields, however, you require many failsafes to prevent damage to your equipment. Also a more expensive method with multiple components.

The easier method is to start the 3 phase induction motor with AC, and simply overspeed it using your prime mover, to begin generating electricity. As you increase the shaft speed, you will notice a decrease in power consumption down to zero, before rising again as you start to export power. We currently have two hydro sites set up like this and haven't encountered a problem since.

 

[looking]

Hey fellas:
I'm actually still alive and just ran across "steelaussy"'s recent post.
For those interested in flare gas or waterpower or even small scale wind net metering; here are my observations.
IT WORKS ...AND IT CAN produce a significant surplus of unused power (that can and does get confiscated at the end of the contract term period) In my case last October 2023 that amount was in excess of 20000kwh's. On top of that, the year of the contract involved continuouslyusing a 15kw electrical heater and aeration fans to decrease the amount of "piggy banked" electrical credits.
In the current contract period there is already >58000kwh's banked despite adding a Ford Lightning and a Chev WT electric vehicle charging to the net metering system.
I'm going to post this an add a bit more below.

A few more comments and with acknowledged help of the

It is much easier than it sounds.

We tried the wind turbine approach with capacitors, rectifiers and solar grid tied inverters. It works well with good energy yields, however, you require many failsafes to prevent damage to your equipment. Also a more expensive method with multiple components.

The easier method is to start the 3 phase induction motor with AC, and simply overspeed it using your prime mover, to begin generating electricity. As you increase the shaft speed, you will notice a decrease in power consumption down to zero, before rising again as you start to export power. We currently have two hydro sites set up like this and haven't encountered a problem since.

Oh the power of the internet. And glad you have a solution that works in your situation.
I too initially tested the same basic system by overdriving a nominal 60 cycle 20hp induction motor with an ac genset. That induction motor was direct coupled an identical motor with its motor leads connected to the grid.

And as in your setup, it worked with simplicity, but in some circumstances I was warned that power production would not disconnect when the grid power went down (has to do with capacitance and potentionally endangering other electrical workers) Of course that can be addressed with contro circuitry that mimics every parameter involved in connecting an additional unit at a utilities generating station.

Long story...short; the only non cost prohibitive reasonable working solution in my case is to use a Certified wind inverter standard (to your country standards).
I'll bring up some interesting stuff about certain wind/solar inverters if interested...and rectifiers for ac to DC conversion if there is any interest