Hi Miao,

Just go through the following steps:

With best wishes.

-Sanjay

@Sanjoy Roy Firstly,I am sincerely very thankful for your kind help.I still have some problems want to ask you.I want to do islanding detection of inverter-based DG by measuring the impedance at PCC. The resulted impedance is used to detect wheather the islanding happened.So,the measuring process is conducting together with  DG's operating.That means there are three sources coexist,DG source,harmonic source and the voltage source act as utility grid.So can you tell me is it work well under this condition?Is there some requirement about the frequency selection about your method?Is the FFT module in PSCAD can used to calculate the FFT of 75Hz component,the frequency which is not integral multiple of 50Hz?I have do such cases,but the result seems not correct.Do you have some good ideas to deal with this or some other means to do the on-line impedance measurement by PSCAD/EMTDC.Waiting for your reply.Thank you very much.

Hi Miao,

Glad to know that my response was of use to you. Please feel free to shoot further questions to me, if required.

As regards your question on whether your way of islanding detection using impedance measure is an effective way or not - well, frankly - I don't know. It seems to be something new that you are trying, and I will be as curious to see the outcome, as yourself !!

As for the base frequency for the FFT in your present simulation, I think you will be playing safe if the frequency of the harmonic source (the one that you will be using) is taken as the base frequency. That way you will be always taking measurements of the fundamental (which will be in your case, same as the source frequency !). The "fundamental" values in PSCAD's FFT is always the one that is the most accurate. So why not use that accuracy feature ??

 You can do the same with a 50Hz base frequency choice, but then you will be looking at a harmonic magnitude, that may not always be too accurate !

With best wishes.

-Sanjay