I want to control the boost converter, found a transfer function but root locus of transfer func. shows that system is unstable so I cant use any controller. I attached the system's transfer func. and root locus diagram and also general transfer func.
If I can make the system more stable, I want to calculate Kp Ki Kd values using the ziegler-nichols method. Can you give me ideas for controlling the boost converter ? and also why PI controller mostly used in converter control ?
Thanks..
Hi Ece Kurt, what are the performance requirements? The desired percentage overshoot, settling time, etc.
Hi Ece Kurt, I'm unfamiliar with the boost converter. Since you have no special requirements, and plant has stable poles, you may try designing an I-Only controller.
s = tf('s');
Gp = (-1.22e4*s + 290)/(9.495e-8*s^2 + 2.826e-5*s + 0.3364)
Gc = (3.5093e-6)/s
Gcl = (Gc*Gp)/(1 + Gc*Gp);
Gcl = minreal(Gcl)
step(Gcl)
Hi Punnya Priya, if PD controller is used in the cascade config and it is not properly tuned, then the non-minimum-phase zeros will become quite large. One way to maintain the status quo of the non-minimum-phase is to use the I-Only Controller.
For the I-Only controller, you can take the following approach:
syms s Ki
Gp = (-1.22e4*s + 290)/(9.495e-8*s^2 + 2.826e-5*s + 0.3364)
Gc = Ki/s
Gcl = Gc*Gp/(1 + Gc*Gp)
Gcl = simplify(Gcl)
From the characteristic equation of the simplified closed-loop system, you can collect the coefficients of the terms and then apply the Routh–Hurwitz stability criterion on the Routh table to determine the critical gain, which is Ki ≤ 2.757156846×10−5 (see attached figure). Later, the integral gain Ki can be tuned according to the desired performance specifications and the Nyquist Plot.
To me, I'm comfortable with the range 2×10−6 ≤ Ki ≤ 6×10−6.
Ok I think that I have a solution for you. Current hysteresis control. Find which is the output current that you want. Calculate (the imagine) current on the converter's coil (from the power equation Pi=Po => Vi Ii = Vo Io). Put same limits (up and down) for this current and generate the transistor's pulses.
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