Questions tagged [control-system]

A system that may be electronic circuits or even software that uses control theory (principally differential equations) to control an output by monitoring various aspects of the system under control and varying inputs all towards meeting a defined goal. Some famous examples are controlling a rockets thrust angle to ensure directional control.

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How can a system reach its steady-state if the I-action of a PID controller, u(t), doesn't go to zero as the system approaches its desired value?

The I-action of a PID controller, which integrates the error over time, results in the control signal: $$u(t) = \int_0^{t}e(T)\text{d}T$$ This means that, when the system reaches its desired value ...
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In practice, what is the difference between the “nominal plant model” and the “plant model”?

I am reading a book on nonlinear control and disturbance rejection, and in many examples, they distinguish between the "plant model" \$G_p(s)\$ and the "nominal plant model" \$G_p(s)\$. They also add ...
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251 views

Meaning of transfer function in s evaluated at a complex number

From the pole-zero plot, you can compute the system frequency response by assuming a locus of test points along the \$j\omega\$ axis. Figure from: http://web.mit.edu/2.14/www/Handouts/PoleZero.pdf \...
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why large signal can make a conditionally stable system unstable?

This image below is from this TI cookbook. Please look at the red box. Question: why large signal can make a conditionally stable system unstable?
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867 views

Unexpected LTSPICE Output - Voltage Mode Buck Convertor

I'm trying to simulate in LTSPICE a simple buck convertor taking 34V -> 20V @ 2.5A and I'm not seeing what I expect. Here is my circuit and some waveforms: The top half of the circuit is the ...
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1answer
2k views

Relationship between switching frequency and controller's crossover frequency in buck SMPS

Context: tuning the control loop of a buck SMPS. I specicifally have a TI TPS40200-based circuit in mind, but I think this applies to SMPS design in general. Quoting from Type 2 compensation network: ...
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Determining whether a system is LTI given response to a rectangle box input

Given a system, it is possible to determine whether the system is LTI given the response to input to the system, other than the unit impulse? Specifically, my input to the system is $$x(t)=\begin{...
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144 views

Is unstable system unstable for ALL inputs?

We define system to be stable if for all bounded inputs, it will give bounded output at all times. But does unstable system means it will have unbounded output for any input? This question is ...
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127 views

How can infer instability from the frequency response of control system?

When can we judge a control system to be unstable from its frequency response?.For example, thermostat computes the error signal (desired room temperature - actual room temperature) and then actuates ...
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Why is this system stable?

I was given the system defined by the open-loop transfer function: \$L(s)=\frac{5(s^2+1.4s+1)}{(s-1)^2}\$ I was told to use the Nyquist criterion to determine stability. Examining the Nyquist plot ...
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Can a controller have a negative gain?

I'm working on a problem that involves a Ćuk converter. The question asks "find k_c (a gain for a controller) such that the system is marginally stable". So I got the properly space-state model with ...
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146 views

Transistor switching instead of acting linearly

I am using a Darlington Transistor (MFG6388GOS) as the controlling element for a Current Controller. The controller has an oscillation which I have narrowed down to the transistor switching. I want ...
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Controlling an Electromagnet using a microcontroller

My question stems from this one here: Controlling an electromagnet strengh with arduino Background I am working on the classic magnetic levitation control systems problem. I have a 10N electromagnet ...
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759 views

Root locus of discrete time system

I have a question about a probably easy task, but I can't find the right K. I have the loop with an adjustable gain element given: $$Q(z) = \frac{H(z)}{1+ K\cdot G(z)H(z)} $$ I have given: $$H(z) ...
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886 views

Why does Nyquist plot only need loop gain but not the entire closed loop transfer function?

I was trying to compare a Bode plot and a Nyquist plot of the same system and realized that I was probably comparing apples to oranges Bode plot is plotting the entire closed loop transfer function, ...
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Mathematical model of the temperature of resistors/heatsinks?

I want to model the transfer function of a resistor mathematically, and am after some resources / tips on if it's possible to do so. For example, if I put 1V into a 1 Ohm resistor, I want to know how ...
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686 views

What is the effect of aliasing in discrete time controller?

Suppose we have a controller whose TF is $$ G(s) = \frac{1}{(s^2+1)} $$ This yields two marginally stable poles at \$ s = \pm j \$ Now let's discretize the controller through z transform, after ...
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Switched Mode Power Supply : Voltage Mode Control and Error Amplifier Output

I am trying to understand how regulation happens on Cycle-Cycle basis in the case of Voltage Mode Control (VMC) and Current Mode Control (CMC). I understand that in the case of VMC, an error ...
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Describing step response in terms of poles and zeros of transfer function?

me and a friend are stuck describing something, we're both coming to terms with using matlab and we're trying to understand the design of a simple control system for controlling the steady-state error ...
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327 views

Block Diagrams with offset in control theory

I have an equation in the form $$y = mx+b$$. In block diagram form, I could draw this with a proportional gain block and a summer. I was wondering if there are some clever tricks where I can make ...
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Measuring tiny voltage variation with Arduino ADC handing the rapid changes in control algo

I'm hoping I can get some advice, I have an industrial laser position sensor from SICK that outputs 0 to 10 volts. I used a voltage divider to scale it down to 0 to 5 volt range, and feeding that into ...
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Help with a Closed loop and zero order hold function ZoH * 1/s(s+a) type

i would appreciate some help in solving this problem, i need to find the transient response for a unit step, i have a brief idea of how to solve, but my graphs in matlab doesnt seem to fit with the ...
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110 views

dc motors to control unmanned ground vehicle [closed]

This is my first large project as an electrical engineering student and I'm working with DC motors for the very first time. I'm working on designing an unmanned ground vehicle that will weigh ...
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Is it possible for two different systems to have the same step response, and vice-versa?

Every time I have had to tune a controller (PID, usually) to a process, I have first matched an equivalent first order or second order model by doing some curve fitting on the step responses; and then ...
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133 views

Why is this second order system difficult to control?

Why is system of the type $$T = 1/(s^2 - 1)$$ Difficult to control using standard control methods? When I look at frequency plots, it doesn't seem to give me any important information as to why ...
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991 views

Getting transfer function from block diagram

I am having trouble figuring out this step in an example question I've been given. I'm supposed to be finding the 'transfer function in the forward path'. This image shows the block diagram (top) and ...
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776 views

how to map a pid controller to a process

How do you "map" the output of a PID controller to a process? Say you have a resistor, a thermometer, and a PID controller. The thermometer provides feedback, and the PID controller can control the ...
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1k views

Time domain and Frequency domain

what is the difference between time domain and frequency domain components? How do these domains differ from each other?
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Difference between online PID and offline PID tuning?

I've been reading about PID control on the internet lately (Wikipedia). I came across the words 'online' and 'offline' in PID tuning. I googled it but couldn't find anything. What does this mean in ...
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767 views

Transfer Function of Non-Ideal Transformer

What is the mathematical relationship between primary and secondary windings? It can be either in the s-domain, or a time domain expression. This expression must contain all realistic parameters, ...
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Finding the impulse response from the integral

I'm trying to solve the part (a) of the following: I know that: $$ y(t) = \int_0^1 \! \delta (t-\lambda ) \mathrm{d}\lambda $$ But I'm not sure how to proceed from that.
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Root Locus in a feedback loop

I'm trying to draw Root Locus by hand from the following block diagram and confirm the result I got from Routh Hurwitz's table: The table of Routh Hurwitz that I got is the following: And from the ...
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62 views

ASIC Solution for Digital Closed loop Buck Converter Control

I am implementing a Closed loop Current Mode Control Buck Converter on a dsPIC Microcontroller which has an output of 3.3V and unregulated input of 5V. I am doing digital control, so I implemented ...
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87 views

Control theory in PLC (programmable logic controller)? [closed]

What is the control theory of PLCs (programmable logic controller)? PLCs fall in category of linear control or non linear control?
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356 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, ...
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728 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 ...
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219 views

What is the relationship between feedforward control and bandwidth?

This is a control theory question, but because there is no control theory stack exchange, I thought this was the closest appropriate location: I've been studying feedforward control system designs, ...
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558 views

PID controller - How is plant equation derived?

During our control systems course we often work on control techniques where the plant equation/state space model is given .However , how are these derived? For example, if I wanted to build a ...
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1answer
654 views

Analog 4-20 mA Output module for Process Control

I am reading a spec sheet for an 8 channal analog output module for process control that says this: Because all current is sourced from within the module using the 24 VDC excitation, current ...
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186 views

How to infer equivalent PID controller coefficients from an existing black box ccontroller?

I have a 2 input, 2 output system that I have recorded in response to 1. steps (actually quasi-steps, with 50 ms rise time + some overshoot), and 2. sine waves from 0.5 to 50 Hz, in both open and ...
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364 views

Is feedforward used in boost converter operating in DCM mode?

Is feedforward used in boost converter operating in DCM mode? I saw some examples where feedforward is used to control boost converter in CCM but not DCM mode. So I am wondering if it can be used in ...
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267 views

Is time-invariant system taking system initial state account?

The time-invariant system is defined as following: If y(t) = (H(x))(t) and y(t − τ ) = (H(x))(t− τ ) Then H is a time-invariant system. Has this definition taken system initial stats account? At t=0 ...
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259 views

What is the correct transfer function of a feedback loop if the summing amplifier has different input resistors?

Suppose I have a circuit below: simulate this circuit – Schematic created using CircuitLab I know the the transfer function of a negative feedback loop is: $$H(s)=\frac{H_1(s)}{1+H_1(s)H_2(s)}...
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How to find the state-variable equations from the signal flow graph of the system?

How to find the state-variable equations, i.e, the state equation & the output equation for the system described by the signal flow graph below?
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Cascading PID DC Motor Position & Velocity Controllers

I'm trying to build a robot with a differential drive powered by two DC motors. First I implemented a PID Controller to control the velocity of each motor independently. Estimated the TF using the ...
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797 views

When the Gain Margin is negative, for what range of frequencies is will the output resonate out of control?

If your system/transfer function has greater than zero gain for the frequency associated with -180 degrees phase, the system is said to be unstable. What does this mean for other input frequencies? ...
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379 views

Is impulse response always differentiation of unit step response of a system?

I was trying to solve a question in which the transfer function of a system was asked, its unit step response being given: $$ c(t) = 1 - 10^{-t} $$ The method that the book followed was to first ...
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882 views

How can I model this linear power system in MATLAB?

For my power system, let us suppose it has the following dynamic model: \$\ x ' = f(x,u)\$. This dynamic model consists of four first order differential equations (see below). Then, I linearized ...
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197 views

How to Design a State Feedback Controller using an algorithm

I'm studying for an exam and am having a great amount of difficulty wrapping my head around this as I have minimal electrical engineering background, and my notes are confusing. I have read a few ...
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2k views

Brushless motor controlled via current source math model

I'd like to model a brushless motor's (BLDC) dynamic response using Matlab. I'm controlling the motor by an Elesctonic Speed Controller (ESC). I'd like to derive a transfer function of such a circuit ...

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