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    Combining of three AC sources of 230V

    Hey,

    Actually, I'm trying to come with a model of combining three AC sources. In this main criteria is to synchronize all these signals to be in a loop. I don't know how exactly to do this. Can I get some hint to proceed on this concept?

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    Re: Combining of three AC sources of 230V

    Hi,

    To me it's absolutely unclear what you talking about.

    Can you post a sketch of your configuration?

    What do you mean with "synchronize"? Voltage, frequency or even phase angle? Why?

    Klaus



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    Re: Combining of three AC sources of 230V

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    PFA, I'm trying to feed my load with three sources. The intelligent system(IS) needs to divide the total load( For example, assume Total amps=6A, IS must make each source 1 &2&3 to take the load 2A each to serve the final load). To achieve this, all the three sources must be in the same loop like same voltage, frequency, and phase angle. I'm not clear on how to achieve this?



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    Re: Combining of three AC sources of 230V

    You can't do it, at least not without some highly complex and mega-expensive equipment.

    Your only practical solution is to convert all the sources to DC, then combine them before using a single inverter to produce AC out again.

    Even if you took the one source you can't adjust, the line AC, it would be impossible to synchronize a generator to it. The generator speed will vary under load so keeping the exact frequency and phase is not achievable. The PV inverter isn't difficult to sync to the line AC but it too would be impossible to sync to the generator.

    Brian.
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    Re: Combining of three AC sources of 230V

    Synchronizing a generator to the grid is well possible, but requires specific generator instrumentation. Small generators are usually not equipped for it. Grid tied solar inverter is more common



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    Re: Combining of three AC sources of 230V

    Hi,

    if you need to adjust: voltage, frequency phase (and additionally source_impedance to maintain equal current) then my first question:
    * Can you do this with all your three sources? I mean: Is it possible?

    Klaus



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    Re: Combining of three AC sources of 230V

    This is similar to the parallel operation of alternators. Need to check Three condition Voltage, Phase Sequence and frequency should be same.



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    Re: Combining of three AC sources of 230V

    I would suggest something along the lines what Brian has suggested:
    -Your main power grid will be your "master" source. Use it as it is.
    -For the solar system, purchase a commercial grid-tie inverter. It will deliver back to the main grid as much power as the solar cells generate, which can be quite variable.
    -For the local diesel generator, if it doesn't have the necessary equipment and instrumentation (which will include anti-islanding protection) your best bet is to convert it to DC (per Brian's suggestion) and then use another grid-tie inverter to feed the power back to the main grid.
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    Re: Combining of three AC sources of 230V

    Hi,

    Is the whole system connected to the power grid?

    Klaus



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    Re: Combining of three AC sources of 230V

    Based on post #3:
    Synchronizing a generator to the grid is well possible, but requires specific generator instrumentation.
    This sounds like a relatively small Diesel generator. While it is possible to use such a generator with a stable inverter output, I have never seen one. All the small ones (including my own 6KVA generator) use mechanical speed governors which are slow to react, often taking several seconds to recover from a load change. Even then the speed is audibly unstable so I would guess phase sync would be virtually impossible.

    I have approx 2.5KW of PV here and the inverter works fine to supplement line AC but in conjunction with the generator it automatically goes into "attempting sync" mode and never succeeds.

    Brian.
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    Re: Combining of three AC sources of 230V

    I have approx 2.5KW of PV here and the inverter works fine to supplement line AC but in conjunction with the generator it automatically goes into "attempting sync" mode and never succeeds.
    That sounds reasonable if the inverter has proper anti-islanding. The generator frequency fluctuation will probably prevent detection of stable grid connection.

    Is the whole system connected to the power grid?
    I presume "Electricity Board AC" means just this.

    Total amps=6A, IS must make each source 1 &2&3 to take the load 2A
    Why? A solar inverter would deliver the available power, whether it's resulting in less or more than 2 A. If there isn't enough sunlight, it can't deliver 460 W, if there's plenty of it, why throttle the inverter? The requirement is beyond the available and useful function of a solar inverter.

    I also agree with the comments about small generators. To steer a grid connected generator, you need separate speed respectively power and voltage control. The latter is only available with a separately excited synchronous generator. After initial synchronization and grid power-on, the generator runs with synchronous speed. Throttle control commands the delivered real power rather than speed, generator excitation controls the reactive power.

    If the generator is an asynchronous machine there's little chance for grid tied operation, instead you'll go for the suggested AC/DC/AC conversion.



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    Re: Combining of three AC sources of 230V

    Agree, AC/DC/AC conversion is definitely the way to go.

    That is exactly how I am doing it myself right now.
    High dc voltage can create a very efficient system requiring relatively low current.
    I combine dc from a mains rectifier, with dc from solar panels, into an inverter to turn it back into ac.

    With just a few diodes, any number of dc sources can be combined.
    Cheers, Tony.



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