Re: How can I fix the error that produces this peak in Bode plot?

Doug Stewart <[email protected]>
Newsgroups gmane.comp.gnu.octave.general
Message-ID <CAAohRsbaRDCybT0aiibUHAy5aJDF=+Q=4FH5sP8+wt8NJJ9i4A@mail.gmail.com>
On Wed, Oct 14, 2020 at 8:19 AM Doug Stewart <[email protected]> wrote:

>
>
> On Wed, Oct 14, 2020 at 8:11 AM Beginner1 via Help-octave <
> [email protected]> wrote:
>
>> <https://octave.1599824.n4.nabble.com/file/t372684/rlocus.jpg>
>>
>> With regard to that zero at +13333.33, I am not familiar with rlocus, but
>> I
>> have plotted it without finding this zero at +13333 in the plot that would
>> make the system unstable I guess, if located on the right side of the
>> plane.
>> Attached I send the plot. Anyway, I also wrote the command [r,k] =
>> rlocus(sys_1_vd), to see the exact numerical value of the roots, but did
>> not
>> find any +13333.33 location.
>>
>>
>> On the other hand,  by obtaining the eigenvalues of the system, they all
>> have negative real part, except for 2 with a very small positive real
>> part,
>> which it may be due to inaccuracies of the calculation. But I think, this
>> has no relationship with the zero you have pointed out to be located at
>> +13333.33.
>>  -757.69960 +    0.00000i
>>   -1487.09047 +    0.00000i
>>     -28.89898 +  318.89945i
>>     -28.89898 -  318.89945i
>>     -25.27902 +  323.48505i
>>     -25.27902 -  323.48505i
>>      -0.00207 +  314.16966i
>>      -0.00207 -  314.16966i
>>       0.01004 +  314.15586i
>>       0.01004 -  314.15586i
>>      -0.00797 +  314.15227i
>>      -0.00797 -  314.15227i
>>
>> How can I see this zero at +13333.33?
>>
>>
>>
>>
>>
>>
>
> [num,den]=tfdata(sys_1_vd,'v')
> roots(num)
>
> This will convert your transfer function  to num/den form then looks at
> the roots of the numerator.
>
>
>
Did you get it working?

Doug
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