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Re: How Tune PID in octave using Frequency Response data

From: N
Subject: Re: How Tune PID in octave using Frequency Response data
Date: Tue, 28 Jul 2020 22:01:34 +0200

> Hello Nicklas,
> I have the open loop frequency response of 1/2 bridge inverter capacitor
> current (using PSIM).  Now I would like to convert that response into a
> transfer function so that I can create the closed loop response (as you
> mentioned).
> I do have an exact transfer equation for the capacitor voltage with respect
> to duty cycle so maybe that can somehow be changed to capacitor current
> since capacitor current equals C*dv/dt. Maybe just multiplying by Cs would
> do it?

Best thing would be to write it down on state space form. As it is an inverter 
I would guess you could modify duty cycle each period and in such case duty 
cycle should be an input and you would make an average model over one cycle, 
there is probably some dead time which may or may not be important. In case it 
is non linear you also to have to linearize around curent working point.

Then written on state space form you could use lqr(...), lqg(...) or acker(...) 
functions in Octave to make you control loop while bode(...) and nyquist(...) 
functions could be used for stability analysis. In cause you did not att dead 
time in state space model you could add a phase delay then stability is checked.

Think I got it correct.

Nicklas SB Karlsson

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