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    current sense across the output of a Grid Tie Inverter

    Current sense at the output side of the Grid Tie inverter is used to sense the presence of the electric utility current across the output for islanding? right?.. where should I connect it?

    my block diagram is an inverter stage then an EMI filter, should my current sense loop be connected in between the inverter stage and the EMI filter? or right after the EMI filter?

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    Re: current sense across the output of a Grid Tie Inverter

    The current sensor should be connected after the EMI filter. i.e. between the Inverter and the utility mains.
    The presence of voltage across the grid is sensed using a PT/or a resistive divider and not by the CT.

    The grid acts as a very low impedance load when you intend to pump current into it, hence it is important that you sense the pumped current so that you do not exceed your system's rated specifications.
    When the grid voltage is available, the inverter is synchronized with the voltage waveform of the grid, current starts getting pumped, and this current is monitored via the CT and fed to your inverter's control loop.



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    Re: current sense across the output of a Grid Tie Inverter

    The current sensor should be connected after the EMI filter. i.e. between the Inverter and the utility mains.
    Not necessarily. In case the sensor is utilized for inverter overcurrent detection or space vector modulation with direct current control, it must be placed on the inverter side of the output filter. The output filter is more than an EMI filter, by the way. It's series inductance is essential when connecting a voltage switched inverter to the grid.

    The presence of voltage across the grid is sensed using a PT/or a resistive divider and not by the CT.
    The OP is asking about islanding detection, which is more than just sensing the grid voltage.



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    Re: current sense across the output of a Grid Tie Inverter

    Quote Originally Posted by FvM View Post
    The OP is asking about islanding detection, which is more than just sensing the grid voltage.
    What are the different methods of islanding detection?
    If we consider rate of change of frequency(ROCOF), it can entirely rely upon the sensed voltage waveform, right?



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    Re: current sense across the output of a Grid Tie Inverter

    If we consider rate of change of frequency(ROCOF), it can entirely rely upon the sensed voltage waveform, right?
    Yes, but others are evaluating the grid impedance as far as I'm aware of.



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    Re: current sense across the output of a Grid Tie Inverter

    I am still a little confused.. i have drawn below a sample block diagram.. this current sense is for anti-islanding purpose.. is it the right location for the current sense? or must I put it elsewhere?

    Click image for larger version. 

Name:	GTI sample BD.jpg 
Views:	9 
Size:	32.7 KB 
ID:	124658



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    Re: current sense across the output of a Grid Tie Inverter

    It seems like the correct place...



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