Questions tagged [control-theory]
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76
questions
-3
votes
1answer
62 views
Pi controller equation problem [closed]
Digital pi controller equation has any problems while implementing in micro controller..Actually i am implementing in tms320f micro controller like control output
$$y(n)=a\ e(n)-b\ e(n-1)+c\ y(n-1)$$
...
6
votes
2answers
915 views
I'm confused a bit on basic control stuff for a PID controller
I'm doing a PID controller demonstration project in which heat is applied to a K type thermocouple and I'm supposed to maintain the temperature read at 50 °C using a PWM signal. I know the basic ...
2
votes
0answers
56 views
Control system — closed-loop system problem
Given a closed-loop system as shown below:
Suppose that \$x(t) = u(t)\$ and \$d(t)=0.5u(t)\$. Determine the output response of \$y(t)\$ and it's steady state at \$t\rightarrow \infty\$.
I've tried to ...
1
vote
3answers
52 views
Nichols plot confusion
The transfer function is \$F(p)=10/(p^2+2p+1).\$
Using Wolfram Alpha, the Nichols plot shows that the argument \$\to -\pi\$ when \$\omega \to +\infty\$.
However, calculating the argument on paper ...
0
votes
0answers
32 views
Feedforward from measurable disturbance
Gff is chosen so that it completely cancels the disturbance (Gff = -Gv/P) and Lp < Lv. Is it easier to control if Tp < Tv or Tp > Tv. I am a little bit lost on how to begin here? Should I ...
0
votes
0answers
46 views
Output of a linear system with discrete feedback
I have this problem here that I had trouble with few years back and I still don't understand
https://imgur.com/At2BbWe
With a T period discretization on the feedback and a first order hold after it.
...
0
votes
0answers
36 views
Linearization of nonlinear plant with system identification in Matlab
I hope this question fits in here and there is someone who can maybe help me.
I am new to control theory and I have a very complex Simulink model which is nonlinear. I want to have a linear ...
0
votes
1answer
60 views
Decide P controller gain K so that phase margin is 50 deg
I need help finding the gain \$K\$ so that the phase margin for the system equals 50 degrees.
$$F(s) = K$$
$$G(s) = \dfrac{1}{(s+1)^2}$$
\$v\$ is a process disturbance sinusoid with amplitude 2.5 and ...
1
vote
0answers
67 views
From where does State space model equations come from?
I have a good basic understanding on classical control theory. Now I am studying modern control theory.I encountered the following equations as seen below.
Online I have only been able to find ...
1
vote
0answers
60 views
fast analytical technique identifying poles/zeros using degree of freedom
I encounter some engineers who can quickly spot poles and zeros in the circuit by identifying "degree of freedom". For example, a typical technical discussion goes like : "a miller ...
0
votes
0answers
81 views
Determine range of proportional gain with given overshoot
I have given the open-loop transfer function
$$
G_{ol} = 1.42 \frac{(s+3)^2+6^2}{(s-1)(s+2)((s+4)^2+4^2)}
$$
The task I was given is determining the range of the proportional gain, which makes the ...
1
vote
2answers
129 views
Tuning PID without transfer function
I'm very new to control theory and I am stuck at PID tuning.
I have a given Simulink model but I do not know the transfer function. I want to use a PID to provide new input from the output of the ...
0
votes
3answers
88 views
Why do I need phase margin if I know the transfer function?
What is the point of examining the phase margin (or gain margin) for a closed-loop system if I can just solve for the transfer function. The transfer function will give any poles and zeros, which can ...
1
vote
1answer
56 views
Linearization of nonlinear system
I have a nonlinear system described by:
$$\begin{align}
V\,\dot x_1 &= Q_1 C_1 - (Q_1+u)x_1 \\
V\,\dot x_2 &= C_2\,u -(Q_1+u)x_2 \\
y &= -\frac{\log{\left[(x_1-x_2)+|x_1-x_2|+4K\right]}...
2
votes
2answers
233 views
Steady-state Error Definition
In the textbooks and reference material which I have been using during my course on control systems, a common definition of steady-state error is as follows:
$$E(s)=R(s)-C(s)$$
where E(s) is the error ...
0
votes
1answer
135 views
Finding the overall transfer function and plotting root locus of a digital control system
I have started to learn about digital control theory and struggling with a particular diagram of a digital control system. The system is presented below:
\$D(z)\$ is a digital compensator, \$G_{h0}\$ ...
2
votes
2answers
281 views
Nyquist stability criterion for positive feedback
it is known that the stability of a system with negative feedback may be analized through the Nyquist stability criterion, which is based on observing the number of turns around the point (-1;0) in ...
0
votes
1answer
51 views
Layman explanation of “dynamics” or “dynamic behaviour”
I often read the term dynamics or dynamic behaviour in electrical engineering especially in control systems course
What is meant by it?
Is it means that the system whose internal state/properties ...
0
votes
0answers
231 views
What will be minimum number of states / state variables for these control systems in state-space model?
Consider the systems as LTI and SISO with transfer functions given below:
I have read that minimum number of states for an LTI SISO system required to represent in state space analysis for any ...
0
votes
1answer
181 views
555 square wave generation with frequency feedback
Knowing that 555's behaviour varies according to temperature, I wondered:
In an astable configuration, is there some way to measure output frequency, compare it with some desired value, and use this ...
1
vote
1answer
71 views
Feedback Circuit schematic to Control Theory block diagram?
I'm studying analog electronics circuit with feedback.
I see that, during analysis, a useful abstraction over the schematic is the block diagram in control theory style, but I stuggle in deriving it ...
0
votes
1answer
24 views
Nomenclature for changing characteristic curve
OK, I'm at a loss for words on this one. I'm looking for a word or phrase to describe the following situation...
I have an open loop control system that when I apply voltage \$A\$ I get output \$A_1\...
0
votes
0answers
205 views
Transfer function with separate time delays in each term
We've been given the problem below for our current assignment
As far as I can recall, I have never seen a transfer function with time units in the function itself, added onto each separate term. I ...
0
votes
1answer
139 views
Looking for a quote on dynamic system identification
Does anyone know of a quote by an eminent control theorist or controls engineer or book author who I could reference who said something along the lines of the following:
The process of control ...
0
votes
3answers
2k views
Effect of RHP zeros on stability
Why do zeros in the right half of the \$s\$ plane reduce stability (i.e., gain / phase margin)?
0
votes
1answer
964 views
Determining Number of states in State Space Modeling
I want to use state space modeling for representing the following circuit system. However, I am unable to decide the number of states. I am able to describe the system with a set of three equations. ...
0
votes
1answer
169 views
How to calculate roots using root locus method? [closed]
Find the roots of the following polynomial by use of the root locus method.
3s⁴ + 10s³ + 21s² + 24s + 30 = 0
(The root locus plot has not been given.)
Can you please help me with this?
This ...
5
votes
2answers
3k views
Integral only control (as opposed to PI or PID)
I am familiar with PI and PID control but I've recently been reviewing code that seems to use I (Integral) only control. What are the benefits of I control over PI control, and when should it be used /...
0
votes
1answer
141 views
Bode Plots - Absolute Value of Complex Function in Magnitude calculation
I'm struggling with one step in the magnitude calculation during manual Bode plotting. Specifically during the step of applying the absolute value to \$s = jw\$, what is the reasoning for why you can ...
0
votes
1answer
58 views
Control system error based on differential process value
In a basic PID controller, you measure the process value y (such as temperature) directly; then the error e is equal to the difference between the process value and the set point r. The error feeds a ...
0
votes
1answer
326 views
Op-amp control theory
back at it again trying to use your genius brains.
I have been trying to teach myself audio amplifier design. The big road block I am getting into is the control theory part of it, meaning how does ...
2
votes
2answers
509 views
Why linearise around an equilibrium point?
In the control theory dealt in class I was taught to always linearise a nonlinear system around an equilibrium point, i.e., where $$\dot x = 0$$
However, linearization is a Taylor series expansion, ...
2
votes
1answer
959 views
Understanding the role of Pole zeros cancellation from the definition of stability
I have encountered the following theorem in a book.
According to me, I can get an asymptotically stable system even if cancellations exist for the unstable poles. my example,
Then Why does this book ...
0
votes
0answers
69 views
Obtaining the analytical expression using the state transformation matrix
I am trying to derive the analytical expression in the box below. T is the state transformation matrix.
x_dot=A*x(t) is a second order linear system.
A has 2 distinct eigenvalues s1 and s2 and ...
0
votes
0answers
485 views
Why gain crossover frequency must be lower than phase crossover frequency for stable systems?
As far as I understood from here, phase margin means the amount of phase that needs to be added in order to coincide with 0 db gain and -180 degrees phase. Likewise for the gain margin it means means ...
1
vote
2answers
63 views
limits of performance
I am trying to understand a topic on limits of performance.
So there is a delay of tau between input and output so the transfer function becomes G(s)*e^-(tau *s).
I am unable to understand the ...
2
votes
2answers
844 views
Should the error term of PID be normalized?
By "normalized", I mean +/-1 ~= the maximum error the system can reasonably be expected to experience, or divided by the setpoint.
Background: I am working on a PID controller for an SSR heater ...
1
vote
1answer
180 views
Transfer function of a digital phase frequency detector
I'm confused about the transfer function of a digital phase frequency detector. Why can we say that the pfd output is proportional to the phase error?
The pfd (with charge pump) generates current ...
0
votes
2answers
374 views
Loop bandwith and open-, closed- loop gain in ADIsimPLL
I'm want to use ADIsimPll to calculate the loop filter properties for a PLL I want to build. I read some things in the programs help topics which I find somehow strange. Maybe you guys can help me out ...
2
votes
1answer
550 views
Connection between PID, Pole placement and LQR
I am trying to control a wheeled inverted pendulum with a PID controller. I already designed a linear quadratic regulator (LQR) and a pole placement regulator (PPR). I would like to design a PID ...
0
votes
1answer
180 views
Definition of minimal phase
Let us consider a linear time-invariant system. The term minimum phase is used for a system that has stable poles and stable zeros. A system is called nonminimal phase if it is not minimum phase.
...
1
vote
1answer
67 views
The system is not completely reachable, Is state x1 reachable from x0?
The system is
$$
x(k+1)=\begin{bmatrix}
1 & 1 & 0 \\
0 & 1 & 0 \\
0 & 0 & 1
\end{bmatrix} x(k)+\begin{bmatrix} 0 \\ 1 \\ 1\end{bmatrix} u(k)
\\ y(k) =\begin{...
1
vote
3answers
188 views
Linear regulator loop dynamics
Given a step change in the input voltage of a standard op-amp based linear regulator, a finite amount of time is needed for the op-amp to sense the voltage difference at its input and do whatever it ...
1
vote
4answers
127 views
Why is a system description in control theory important?
If you want to control a system (with a loop controller), why actually do you need to know anything about the system itself (its dynamics or the transfer function or impulse response or whatever)? Isn'...
0
votes
1answer
296 views
Pure transport delay? (Nyquist plot)
How does pure transport delay affect the Nyquist plot, and how is it possible to find the maximum value of the delay, such that the system stays stable even after delay is introduced?
0
votes
2answers
694 views
Why can't a first-order block have an oscillatory step response?
From what I understand, multiple-order blocks can have step responses that oscillate.
It's apparent that a first-order block cannot have an oscillatory step response.
How come?
Is it due to the ...
11
votes
3answers
8k views
Why do we use step response? [duplicate]
We tend to identify systems more often by using the step response. Why? Especially when the impulse response is directly related to the transfer function?
0
votes
0answers
148 views
Tips for solving difficult block diagrams?
I've gotten the hang of solving block diagrams, i.e. condensing them to a transfer function. I'm aware that one may be solved in multiple ways.
For simple diagrams, it's fairly straightforward to see ...
3
votes
6answers
799 views
Are oscillators always non linear?
From linear systems theory, self-excited sustained oscillations are only possible by means of a marginally stable system, where poles are located exactly on the imaginary axis. However, such a ...
0
votes
1answer
205 views
Get transfer function from state space
The following system is given and I'm asked to find the transfer function $$\frac{Y(s)}{U(s)}=G(s)$$ $$\bar {\dot x}=\begin{bmatrix} 0 & 1 & 0 & 0 &0 \\0 & 0 & 1 & 0 & ...
