Why does the debux module generate an error message 'Signal name' signal 'doesn't match with the signal name' vabc1 'specified at port' 1 '？

I want to separate the three-phase signals because I want to obtain each phase signal separately, but there are several issues when using the Demux module. Firstly, I don't know what logic Demux uses to separate signals or waveforms. For example, if I choose two outlets for a three-phase signal, what would happen? Or can Demux only be used to separate complex signals into different single signals instead of single-phase signals as I understand them? Secondly, I have no idea what caused the error, as it also occurs when using bus selector. I think it may be due to some settings being problematic? Should we still choose a more suitable module?

Answer 1

[Shubham]

Hi Peter,

I understand that you are trying to separate a three-phase signal using the Simulink “Demux” block and are encountering the error - “Signal name 'signal' doesn't match with the signal name 'vabc1' specified at port 1“. Furthermore, you are seeking assistance regarding the following queries:

• What logic does “Demux” block uses to separate signals or waveforms?
• How can you resolve the error you encountered while running your model?

Addressing your first query, when using the “Demux” block to extract elements from a vector input, we can use positive values in the “Number of outputs” parameter in “Block Parameters” to specify exact sizes for some outputs and ‘-1 ‘to let the block dynamically determine the size for that port.

Here is how it works:

If you have a vector ‘[a, b, c, d, e]’ and configure the “Demux” block “Number of Outputs” parameter with [2, -1, -1]:

• The first port will get 2 elements ([a, b]).
• The remaining 3 elements ([c, d, e]) will be evenly distributed among the other two ports ([c, d] and [e]).
• If you are not specifying output size configuration, “Demux” evenly distributes elements among all the ports. E.g. if you have [a b c d e] and 3 ports, ([a, b]), ([c, d]) and ([e]) will be distributed among the ports.

Refer to the following documentation link of “Demux” block for more detail:

https://mathworks.com/help/releases/R2022b/simulink/slref/demux.html

Regarding your second query, the error you encountered can be resolved by ensuring the following steps:

• Ensure that input signal to the “Demux” block is a correctly formatted vector. For a three-phase signal, this should be a 1x3 vector. Also, ensure that the names of the signals should match exactly what the “Demux” block expects.
• Set number of outputs of “Demux” block to 3. If you configure it for two outputs, it will not know how to handle the third element, leading to errors.
• If you are using a "Bus Selector", ensure that the bus contains the signals you are trying to select and that the signal names match exactly.

Hope it helps.

Regards,

Shubham

[peter]

@ShubhamThank you very much for your help. You explained it very clearly, which was very helpful to me. I will immediately put it into practice and try it out.

Answer 2

[Ayush]

Hi Peter,

From the problem that you have described, it looks like the error that you are encountering is mostly driven from the bus selector that you have mentioned as well. This error is due to the discrepancy in the provided name specified to the "Bus Selector" block, in your case "vabc1", to get input from as it extracts the elements you select by name from the input bus hierarchy. You can also refer to the documentation page to understand more about the functioning of the "Bus Selector" block:

https://www.mathworks.com/help/simulink/slref/busselector.html

Additionally, to understand how the "Demux" block would separate a complex signal in your case a three-phase signal into the desired number of output ports and separate the signal as specified by the user. You can refer to the following documentation to know more about how to "Extract Vector Elements Using Specified Output Dimensions":

https://www.mathworks.com/help/simulink/slref/demux.html

Hope this clarifies your understanding for Demux and the aforementioned error!

[peter]

@AyushThank you very much for your suggestion.I will carefully review the document for learning.