dynamics - variables - time

asked 2014-11-27 05:19:47 -0600

Javier
29 ●4 ●5 ●9

Hello,

Please does anyone know how to obtain the value of the variables in function of time in dynamic simulation?

For example, if I have VAR(L+12) at time "t", i would like to use the value of VAR(L+12) at time "(t-T)" and use it.

One option is to save the variable values at previous time in other variables, but I was wondering if there is a more direct method.

I have not found this information in the user's manual.

thank you. Javier

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answered 2014-11-28 03:10:51 -0600

Arjen van der Meer
26 ●2

updated 2014-11-28 06:34:07 -0600

I presume you'll need them for inside a dynamic model and not for generating the simulation output.

As far as I know, PSSE doesn't offer functionality for using variables from previous time steps in dynamics models. However, many internal variables are based on previous calculation steps (e.g. STATE, STORE), so you could use them to regenerate the variable you want at t-T. This only allows you to use the previous time step, so t-DELT

Alternatively you could as you already mentioned generate a data structure (e.g. ring buffer) inside the VAR array. The http://en.wikipedia.org/wiki/Circular_buffer (wiki) on circular buffers could be a good starting point.

Be careful about how and at which moment in the integration routine the values inside this buffer are set, because the models are called multiple times per time-step or even multiple times per specific MODE.

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Dear Arjen, Thank you for your answer. It is useful to know that PSS/E does not allow to use variables from previous time steps. It is a pity that those values are not accesible, because they must be in some place internally!!! I will do something similar to your recommendations.

Javier ( 2014-11-28 05:51:33 -0600 )edit

I am not familiar with the second option that you propose. How do you create a data structure with a VAR in PSS/E? thank you for your help javier

Javier ( 2014-11-28 05:51:53 -0600 )edit

Dear Javier, The internal arrays like STATE and STORE are overwritten by the simulation routine when the time advances one step. See CH 12-13 of the program application guide for more info. If you select an element from e.g. STATE as an output, the results will be stored in a separate output array.

Arjen van der Meer ( 2014-11-28 06:26:00 -0600 )edit

Ok, thank you very much. I will study doing what I need using that option.

Javier ( 2014-11-28 12:36:05 -0600 )edit

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answered 2015-12-28 07:17:21 -0600