How can I find initial states for simulation?

Hi,

I'm working with an identified MIMO model (4 inputs, 9 outputs) from System Identification Toolbox (I used collected data), I have found and OE model, transformed it on a SS if idss command and I want to use it with Idmodel Block in Simulink for simulation of a new set of inputs. I can't use findstates to set the Initial States, since is another set of inputs and I have an unknow output. How can I find initial states of the SS model to run a simulation with different inputs?

Answer 1

[Rajiv Singh]

Initial states show the effect of the environment on the system. They are not a property of the system to be determined uniquely. You need to ask yourself, what you think the system had been doing up until the time the input was injected into it. Was it at complete rest before then (use zero initial conditions), or do you think it was in some sort of steady-state, like a periodic oscillation (in which case you can create some artificial reponse data and use data2state).

Just like you have the freedom to apply any input to the system, you have the freedom to pick any initial states too.

[Victor Scarano]

Hi Rajiv, thank you very much for the answer! In the case, I'm working on a system model of an oven, so for the initial states I just need it to be the ambient temperature. I used the SI toolbox to find a state-space model on observability canonical form. With a simpler C matrix I was able to use a vector with the ambient temperature as the initial conditions and run the simulation with different sets of inputs.