# Questions tagged [control-theory]

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3answers
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### 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?
2answers
160 views

### Types and regulation schemes LDOs

LDOs, or low-dropout linear regulators, come in various types, but it can be difficult to distinguish them, and to the novice engineer, this regulator is often made to seem deceptively simple. Some ...
6answers
542 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 ...
2answers
856 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 /...
1answer
188 views

### I want to find $\frac{\hat{\theta}}{\hat{T}}$

I have the following block diagram, and I want to find the transfer function $\frac{\hat{\theta}}{\hat{T}}$. I am not sure how to do this, I've got the rules of connection in a series or parallel, ...
4answers
630 views

### Intuitively, why does gain margin and phase margin infer instability in feedback system?

On MATLAB https://www.mathworks.com/help/control/ref/margin.html, gain margin and phase margin are additional gain in the system and additional delay in the phase of the system such that the system ...
2answers
115 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, ...
2answers
449 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 ...
1answer
217 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 ...
2answers
469 views

### Closed loop transfer function problem

Let's say we have the basic feedback system of the picture We know that the closed loop transfer function is given by $$T(s)=\frac{G(s)}{1+G(s)H(s)}$$ Now, the diagram above is equivalent to an open ...
3answers
690 views

### Steps to hand draw Bode magnitude plot for a particular transfer function

Can anyone guide me through how to hand draw a correct Bode magnitude plot for $$G(s) = \dfrac{48000}{s(s+0.1)(s+100)}$$ Don't even need phase plot, just need correct magnitude plot As few ...
4answers
122 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'...
2answers
997 views

### What happens when P controller's gain equals zero?

For example, I use Routh-Hurwitz Cirterion to examine the following system with P controller gain $K$: $$\frac{{K\left( {2 - s} \right)}}{{{s^3} + 3{s^2} + 5s + 3}}$$ I closed loop it with $H=1$ ...
1answer
133 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 ...
2answers
2k views

### Sensorless driving of 3 phase BLDC motor for gimbal applications?

I have started to work on a project of mines, which consists in implementing the stabilization of a single axis gimbal using a generic microcontroller (STM32 or Arduino Uno). The gimbal axis is ...
1answer
4k views

### Difference between a controller (e.g PD) and a compensator(e.g Lead)?

Really.What is it?Can't find anything anywhere related to it...Please don't give fancy examples.Just tell me the difference
2answers
62 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 ...
3answers
115 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 ...
1answer
140 views

### Root locus problem

The problem consists of two questions: a) Find k so that one of the roots is at s=-2 $$(s+1)^5+k=0$$ b) for the value of k you just found find the rest roots using root locus. Regarding the first ...
2answers
1k views

### Stability & error from nyquist POLAR plot?

I have been given the following Nyquist polar plot of an unknown transfer function, along with the fact that this system is openloop stable: Now I can directly see this is a type 1 system. - So there ...
3answers
190 views

### Bode plot of transfer function?

I am having trouble where to start an attempt at sketching the Bode plot for the following transfer function: I know I need to rewrite it into its proper form, making both the lowest-order term in ...
1answer
1k views

0answers
65 views

### Digital PLL reference noise rejection

I have a fully digital implementation of a PLL. The problem that I have is the white noise coming from the PFD (you can view it as input jitter). I would like to filter it a lot, but an implementation ...
0answers
112 views

### a linear system is a bilinear transformation of anyone its circuit elements

I am reading about dissection theorem and the part below is a bit confusing. Could anyone one explain it? Any transfer function of a linear system is a bilinear transformation of anyone its ...
3answers
113 views

### PID Control: Controller of the type $\dfrac{1}{s+k}$

In PID control an integrator action is represented by $\dfrac{1}{s}$ Does anyone know what would be the effect of using $\dfrac{1}{s+k}$ instead of $\dfrac{1}{s}$, where $k$ is a constant? ...
1answer
120 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 ...
2answers
183 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 ...
1answer
51 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 ...
3answers
209 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)?
2answers
110 views

### MATLAB: Pole at 0.1 rad/s contributing to nothing on the Bode Plot - Why?

Consider the transfer function $$G(s) = \dfrac{48000}{s(s+100)}$$ The Bode plot is given as Now observe that the gain at frequency w = 1 Hz is 53.6244 dB. Completely reasonable, because this is ...
2answers
250 views

### Is the Nyquist plot a plot of Re(G(s)) v.s. Im(G(s) or Re(G(jω)) v.s. Im(G(jω))

It seems that people in control theory are divided over whether the Nyquist Plot/Diagram (that is the plot, not the contour!) is a plot of $$\text{Re}(G(s)) \text { v.s. } \text{Im}(G(s))$$ or \text{...
1answer
2k views

### How to find system overshoot (Mp) from Bode diagram

In some questions (in linear control theory) it is desired to design a controller to change the system overshoot (Mp), my question is: Is it possible to find Mp or damping factor directly from Bode ...
1answer
74 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 ...
1answer
106 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. ...
1answer
49 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 ...
1answer
118 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. ...
1answer
199 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?
1answer
1k views

### Overshoot percentage of a critically damped system

My textbook explains how we recognize an underdamped , overdamped or a critically damped system and all their characteristics. Later on, in another chapter, without going into much detail I'm given ...
2answers
73 views

### Stochastic optimal control different in finance and engineering [closed]

What is the different between stochastic optimal control approach in finance and engineering? Why methodes used in finance approach like Ito calculus are not used in engineering?
0answers
71 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 ...
0answers
47 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 ...
1answer
20 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\...
0answers
26 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 ...
0answers
26 views

### How to treat poles with imaginary part when using root locus angle criteria - what is the angle to use?

Context: In the process of designing a phase-lead compensator for a system, I have used the design requirements to find the ideal locations for my closed-loop (CL) poles, have picked a place for a new ...
0answers
174 views

### Design of a lead compensator with root locus in matlab

For the transfer function G(s), I tried to design a lead compensator for the function to have a response to the step with the following specifications: Overshoot= 10%; Ts (2%) = 5s. When I simulate ...
1answer
160 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 ...
0answers
407 views

### Speed of response and crossover frequency relationship

In SISO(Single Input Single output) cases, My professor keeps mentioning the speed of response and crossover frequency interchangeably. I don't really understand what the speed of response means also ?...