State space

[asad1111]

the general form of state space output is y=cx+du which means that output is linear combination of state variables and inputs my question is can we write output in this form when our output is not combination of state variable for example in rlc circuit state variables are vc and IL now if we want to take output 'voltage across resistor' how can we represent it in form y=cx+du

[Floid]

Use the phasor equivalents for the circuit (capacitors = 1/sC and inductors = sL) and figure out the transfer function of your circuit (Vo/Vi). Then convert the transfer function to state space form and you will be able to break out the A, B, C, D parts.

[asad1111]

okay but how will you explain it to anybody by looking at output equation y=cx+d when output is merely combination of state space variables

[Pablo Verdugo]

I'm a total newbie on this, but from what i've read, you need to express all variables as a state space variable if you want to use them in a state space form. For example, when you want to incorporate an excitation system into a SMIB model, you have to express the variables of the excitation system as a function of state variables. (Kundur Chapter 12) But like a said i'm a total newbie.