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Testing a Grid Tie Inverter on a Bench PSU

Discussion in 'Renewable Energy' started by Jules_Theone, Aug 9, 2012.

  1. Jules_Theone

    Jules_Theone Member

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    I want to check how a 350W GTI operates at different voltages and currents. I'm assuming there is some intelligence inside GTIs, even the cheapo Chinese ones which will monitor max power point. But if I'm feeding it a constant voltage or current it should behave a certain way? Can anyone explain the operation of a GTI?

    Thanks,

    Jules
     
    Last edited: Aug 9, 2012
  2. Sceadwian

    Sceadwian Banned

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    It's just an inverter that's synchronized with the mains supply. I guess you could say there's intelligence inside especially if a micro controller is involved but there are feedback methods that are comparatively 'dumb' that work as well.

    Just observe the voltage/current tolerances and test to your hearts content. Most power sources used for GTI's solar/wind/battery do not have square edged transitions when power dips or spikes though, they're rapid but not instantaneous so be wary of extreme voltage changes that might be imposed by a bench supply, you need to make sure there's some kind of slope to changes (especially at high powers) otherwise the control loop for the inverter might do some bad things.
     
  3. RCinFLA

    RCinFLA Well-Known Member

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    GTI treats the DC input as if it was a voltage limited current source. Within the working DC voltage range of the GTI it will continue to increase the load until the voltage starts to collapse on the power supply (or the GTI reaches it maximum power limit).

    Since any current limited, voltage regulated bench power supply has a relatively abrupt current limit foldback, the GTI inverter will likely oscillate irratically trying to maximize power draw.

    You might put a power resistor in series with PSU to make it look more like a PV panel V-I response.
     
    Last edited: Aug 12, 2012
  4. dave

    Dave New Member

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  5. Jules_Theone

    Jules_Theone Member

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    Would it be simplest to use a 500watt transformer with a bridge and cap and the voltage should decrease with increasing current? I wanted to leave it going for several hours to test if it overheats or not. Also do you think that the GTI will "know" it's reached it's maximum power capacity or will it just keep drawing current until the fuse blows?

    Thanks,

    Jules
     
  6. RCinFLA

    RCinFLA Well-Known Member

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    You need a near constant current output with a soft voltage limiting high end. To hard a voltage cap and the GTI inverter cannot react fast enough and over does the loading, then cutting back excessively when PSU voltage collapes.

    The best solution short of a specially design PSU would be to set the PSU current limit as high as possible but not exceeding the GTI input current rating, Then set PSU voltage higher then expected equilibrium with a series power resistor that represents the slope of a real PV panel's high end fall off slope. Instead of a resistor you could put a number of 10 amp diodes in series with power supply output where the number of series diodes represent the number of cells in a PV panel. (36 to 72 are typical range depending on panel voltage rating)

    Do a little reading on PV cells to understand how they work.
     

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