SMA Tripower with highly unstable grid

I am designing a PV system (30kW) to be coupled in a location where utility grid is highly unstable (fluctuation 190v to 230v), with up to 30v difference between two different phases.
I have chosen to use two Tripower 15000TL inverters from SMA.
I would like to know if I have to use a voltage stabilizer or maybe the inverters are able to withstand such variations without tripping-off. Can I program such wide range for tripping threshhold?

Mentionnend in the inverter's tech data:

Nominal AC voltage range 160 V - 280 V
AC power frequency / range 50 Hz, 60Hz / -6 Hz ... +5 Hz

Could you please advise?

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: SMA Tripower with highly unstable grid

    I am guessing that you are somewhere around Lebanon?

    First question is--What is the requirements of your utility and their engineers? Adding power from distributed sites (such as grid tied solar) will probably not make their job of stabilizing the grid power any easier.

    Once you have answers to the above questions, then you would have to ask SMA (or your local SMA distributor) about reprogramming the inverters to meet the local requirements.

    I would think that they can do it--within their design limitations.

    Adding voltage stabilizer(s) between the grid and the GT Inverter might make things even more difficult (from control theory, make the system "unstable").

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • AdPower
    AdPower Registered Users Posts: 3
    Re: SMA Tripower with highly unstable grid

    Hello Bill,
    First of all, I should say that I owe you respect for guessing that I am in Lebanon! how did you do?!! don't tell me there is nowhere else in the world with such a bad grid?!!!

    That being said, the answer to your question is that all utility requirements are to have anti-islanding, to be UL 1742 listed, and VDE V 0126-1.
    It may seem very odd, but that's because Lebanese utility operator has NO experience with ditributed generation, but much work is underway.
    So I actually don't have to worry about utility requirements, I have to adapt to utility voltages and frenquencies.

    So technically, would it be possible for the inverter to feed in to such grids?
    I also would like to add another issue, are there known effects of frequent power outages on the inverter?

    Regards,
    Ad
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: SMA Tripower with highly unstable grid

    Hi again Ad,
    AdPower wrote: »
    Hello Bill,
    First of all, I should say that I owe you respect for guessing that I am in Lebanon! how did you do?!! don't tell me there is nowhere else in the world with such a bad grid?!!!

    I had one person here really confused when I said I could tell by the "accent" from their post. :p

    But, in reality, everyone who posts/visits anywhere on the web leaves their IP Address behind. IP addresses can be linked back to the hosting company and/or other services that guess at locations (people filling out forms on web, or other methods?). The two that I usually use are:

    http://whois.domaintools.com/ (listed your ISP out of Lebanon)
    http://www.geobytes.com/iplocator.htm (about 95% accurate--but in your case, it returned New York)

    We try to respect other's privacy, but at times, knowing a rough location can help answer a post more quickly without a game of 20 questions.
    That being said, the answer to your question is that all utility requirements are to have anti-islanding, to be UL 1742 listed, and VDE V 0126-1.
    It may seem very odd, but that's because Lebanese utility operator has NO experience with distributed generation, but much work is underway.
    So I actually don't have to worry about utility requirements, I have to adapt to utility voltages and frequencies.

    For background--My way of describing a GT inverter is that it "follows" the AC Voltage wave form of your utility voltage, and simply "injects" current in to the utility connected wiring--The power going to supply local loads, or even back out the to the grid (spinning the meter backwards) and sharing energy with others in your local area. The inverter is simply using the equation of Power=Voltage*Current... So, whatever the utility voltage is at any instant, the GT inverter is measuring the power available from the solar array, and outputting current back into the grid to satisfy that equation (note: In this case the GT Inverter looks like a "Current Source"--You can connect current sources to a Voltage Source, like the utility grid, and pump energy back into the grid). That way, the GT inverter is not "syncing" with the utility generators the way a (for example) large diesel generator would on your property. The diesel genset would have to rotate at exactly 50 (or 60) Hz and be exactly in the same phase--The the switch to connect the two together is turned on. And now, the genset is locked to the utility power, and the more fuel you supply the diesel motor, the more current is pushed out to the grid (in theory, if you cut off the fuel to the diesel, the alternator will continue to spin the motor/alternator at speed--consuming power from the grid). From the "outside" GT Inverter and a synchronous generator set look the same, from the inside, they are quite different in control theory.

    For all the world, the "GRID" looks like a giant AC battery to the GT Inverter.
    So technically, would it be possible for the inverter to feed in to such grids?

    Yes, the inverter would not "care"--As long as the grid voltage/frequency is within its design range. The UL/VDE/etc. requirements are there for "safety"... In various conditions, the utility wants the GT Inverter to turn off quickly (within a few cycles) so that there is not damage or "hot power lines" if the utility cuts power (electrocute somebody) or something else goes wrong.

    So, the voltage/frequency tests are there to ensure that the GT Inverter(s) do not supply power into a failing grid (say 3 phase, and the utility drops a phase with a transformer or fuse failure, the code requires that all GT supported phases be turned off too--as I recall).

    This "sensing" feature has now been used in various applications. For off grid power, you can connect a standard Sine Wave inverter to a battery bank and create a "local" or "micro" Grid. Then you connect the GT Inverter+Panels, and the GT Inverter will share the loads, or if there are not enough loads, (in many cases) can "back drive" the Off Grid Inverter and recharge the battery bank.

    The batteries could become over chargred (OG inverter has no way of controlling battery charging in the case with a "standard" OG Inverter), so what they did is to have the OG Inverter very the frequency by 0.5 to 1.0 Hz or so--Which would then cause the GT Inverter to shutdown with a 5 minute time out). When the batteries needed charging again, the OG inverter would go back to normal frequency, and the GT Inverter would start up again.

    SMA went even a step further.... They vary the frequency from standard (+ and - Hz, so that clocks would keep time accurately) a proportional amount. This would signal to the GT inverter to reduce its total output power to that amount required by the OG inverter to keep its battery bank properly charging.

    For utilities, there is the possibility of "too much" solar/wind power--A few are now starting to vary their grid frequency so they can "knock off" distributed generators before they "lose control" of the grid frequency/voltage levels.
    I also would like to add another issue, are there known effects of frequent power outages on the inverter?

    For the GT Inverter--Not much--They typically have a five minute "time out" where they wait until the grid "is good", wait 5 minutes, then start up and do their GT Solar thing.

    For the Grid, a "large" GT Solar (or Wind) system can cause all sorts of issues... The local voltage can start rising (problems in Pueto Rico with that and a US military base with solar), or the the "reverse power flow" can exceed the local transformer/distribution wiring capacity (a large housing development was turned down for solar power on every home without having to pay the utility serious money to upgrade the local distribution network). To large wind farms and long distance transmission lines (NE US, Texas I believe).

    My guess is that when the local GT Solar/Wind reaches about 10% of the local capabilities (transformers, distribution lines, small grid power systems), then there will be serious issues for the utility engineers to address.

    GT Inverters don't have the "rotating mass" of a large alternator (or power plant)--So they are not "affected" by frequency/phase issues.

    But at the same time, GT inverters do not add to grid stability, and there are some other issues too such as "power factor"...

    Power factor
    - Wikipedia, the free encyclopedia


    Basically, a GT Inverter is (usually/always?) programmed to supply a PF of 1.0 ... That is the voltage and current wave forms are always in phase and a "perfect" sine wave (5% or less total harmonic distortion).

    Real loads vary from 1.0 PF (resistance heater, power factor corrected motors, computer power supplies, etc.) to around 0.67 or even 0.50 PF (induction motors, non-PFC power supplies, or even CFL --twisty florescent lamps).

    This means that the utility still has to supply the current that is not pure sine wave in phase with the voltage. And this causes the utility to still run their large generators (technically alternators) to supply part of the "apparent power" to run these types of loads. This gets into a whole bunch of complex AC circuit design/math. And even into billing (in the US, we pay for kWH, not kVA or "apparent power")--So the utility does not even get "paid" for this current they are supplying (commercial customers do pay for kVA in some form or another--usually as a "penalty" on their bills for having "bad" power factor).

    This is a complex issues--And is usually ignored for smaller GT systems (typically under ~10KW in North America)--But is a real issue for utilities.

    Sorry for the long answer to short questions.

    -Bill "I will stop typing/linking now" B. :roll:
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • AdPower
    AdPower Registered Users Posts: 3
    Re: SMA Tripower with highly unstable grid

    Wow, a big big thank you Bill! I hope I will be in place to help you some day ;)

    Your explanations are great. I had already contacted SMA tech and they said the same thing: they can get me to program large range thresholds for the AC Voltage. They also said that unbalanced phases is not an issue, it can be taken care of by inverter programming software.

    Hopefully I will keep you updated

    As for the IP location, I should admit I didn't think abt it, I didn't even pay attention to the fact that you're a moderator with "look around' capabilities ;)

    Regards,
    Ad
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: SMA Tripower with highly unstable grid

    You are very welcome Ad.

    And don't be a stranger. It is always interesting to here what others are doing around the world.

    Take care,
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset