potential design mistake impedance measurement block

Hi Matlab Support Team and everyone,

when the impedance meas. block is connected to a bus with two inducative load connected to the same bus the frequency results becomes very strange.

Please give it a try and build a simple network. tow inductors in parallel and the impedance measurment block will calrify my concern.

Thanks in advance.

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Answer 1

[Asvin Kumar]

Looks good to me.

Here’s the model I’ve tried with identical Parallel RLC branches having values: R = 1e9 Ohm, L = (1e-1)/(2*pi) H, C = 1e-12 F.

Here are the results I’ve got for the parallel case and singular case:

Both these results match theoretical expectations.

You might have missed adding a large resistance across the nodes of the Impedance Measurement Block. Omitting this resistance distorts the Impedance and Phase responses. Have a look at the Limitations of the block at https://www.mathworks.com/help/physmod/sps/powersys/ref/impedancemeasurement.html

It reads:

If you plan to connect the Impedance Measurement block in series with an inductance, a current source, or any nonlinear element, you must add a large resistor across the terminals of the block, because the Impedance Measurement block is simulated as a current source block.

I have attached the model I used to verify this with this Answer. Have a look.

[tha alg]

Thanks Kumar, I think you have made a clear statement about the resistance. Although a large impedance of 100e12 was used to comply with large resistance recommended, I found 1e3 was enough to obtain the impedance scan with no distortions.

Best wishes