11 votes
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Block diagram vs flow chart?

Use Google's define:<item to look up> feature. block diagram noun: block diagram; plural noun: block diagrams a diagram showing in schematic form the ...
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  • 8,429
9 votes
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How does one become a control systems engineer?

To a large extend the answer depends on the industry. For example if you work for a large aerospace company it might take a while before you can get chance to get involved in designing a control ...
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9 votes
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How can I approach the application of control theory to real control systems?

I hope I can help you in some way, your question bounces around a bit so I'm guessing a little on what you are wanting to know. This is how you come up with a controller that is implementable from ...
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9 votes
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Is nonlinear control slower than linear control?

"Linear" imposes a set of restrictions. "Non-linear" simply means there are no restrictions. Many non-linear control schemes can be faster than linear ones. Linear control schemes are restricted to ...
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  • 11.3k
8 votes
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How do you set up a PID-Control if the time constants of the controlled system are variable?

One way would be to implement some form of adaptive control. If your range of time constants is small and known, you could use something called "gain scheduling" where you determine before hand all ...
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8 votes

Minimal realization of a MISO system

One way of doing this is using the Kalman decomposition. For this you need the reachable and unobservable subspaces. These subspaces can be constructed using the image of the controllability matrix ...
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  • 1,603
8 votes

If a control system is unstable does it mean it will oscillate?

An example of control system with non oscillatory response. $$ \frac{d x}{d t} = 0 + u\\ u = x $$ Closed loop equation of this unstable system is $$ \frac{d x}{d t} = x $$ and its response is $$ x(t) =...
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  • 626
7 votes
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Causal and Non-Causal PD Controller

Because with the form: $C(s) = K_ds + K_p$ you have a non-proper transfer function. In process engineering, you always need to have proper transfer functions, where the degree of the numerator is ...
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  • 1,806
7 votes
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Feedback control of two-link planar manipulator

Convert the nonlinear model to state-space form, $x'=f(x,u)$, and linearize it to get a linear state-space or transfer function representation. You can use this to design a PID controller and simulate ...
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  • 1,876
7 votes
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Why is it impossible to create an observer for this not fully observable system?

Observability means that you can estimate the complete state using only the output, without knowing the initial state. In other words, you have to figure out where you are without knowing where you ...
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7 votes

How are bode plots drawn for unstable systems with time delay?

You are absolutely right. Since the magnitude is the absolute value of the complex function $F(j\omega)$ the plot does not change with the sign of the pole or zero. The Phase on the other hand does ...
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  • 71
6 votes
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When are overshooting controllers preferred over asymptotic ones?

For some systems, the salient criterion is settling time to within some error band. Sometimes you can get faster settling by allowing earlier overshoot. If you need a system to get to within some ...
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6 votes
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In Control Systems Engineering, why do imaginary poles and zeros on the LHP indicate stability?

Only the poles in the LHP are necessary for stability. This is because the transient response of a LTI system will consists of a linear combinations of $e^{p_i t}$. If a pole is complex, $p_i=\rho_i+i ...
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  • 1,603
6 votes
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Advantage of anti-windup

Anti-windup is a concept for feedback controllers with integral terms, e.g. PID, to keep the integral term from „overcharging“ when regulating a large set point error. It basically saturates the ...
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5 votes
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Determine the range of values for a PI controller

There is a mistake in your expressions. The coefficient of $s$ is $2+k_p$. The conditions are: $$\frac{1}{3} \left(3 \left(k_p+2\right)-k_i\right)>0$$ $$k_i>0$$ $$k_p>0$$ This simplifies ...
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  • 1,876
5 votes

Controllability of $x' = Ax + Bu(t)$ implies controllability of $\left \{ \begin{matrix} x' = Ax + By \\ y'=u(t) \end{matrix} \right.$

The solution is fairly straightforward. Short answer The system is controllable without any modifications. You made a small mistake calculating the new controllability matrix: you are missing the ...
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5 votes
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Second order system with additional pole

I think there must be some other restrictions placed on your professor's comment. Adding a pole to a general second order system makes it a third order system and the dynamics can change dramatically....
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5 votes

Why can't proportional gain alone, reduce the error to zero?

To understand why proportional gain won't drive the error point to zero, it is best just to look at the math. Consider the PID loop shown in the image below. The loop algebra in the $s$ domain comes ...
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5 votes
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A stable transfer function which diverges?

Without any more info, I think your problem arises from the values of $a_0$ and $a_1$. The answer is a little involved, so a bit of systems background is necessary. The short answer Your system should ...
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5 votes
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Continuous time and Discrete time systems

A controller is built around a physical system. What is the open-loop behavior of the system? You have to sample the physical (continuous-time!) system in order to provide feedback to your discrete ...
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  • 3,525
5 votes

Quaternion in control applications

Euler angles are easier to understand and use. Imagine a airtrafic controller getting a aircraft heading info as quaternion data. Euler angles are significantly easier to understand interpret and ...
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  • 3,425
5 votes
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Square wave transfer function?

I thought I would expand a little on the answer offered by Karlo. Long story short, I would not try to calculate the analytical time response of a system to a square wave. That would be a serious ...
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5 votes
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Which course to take? Optimal control? Nonlinear control?

In nonlinear control theory, you will recognize most concepts such as controllability and observability where the linear case is often a special case of the nonlinear case. I would highly recommend ...
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  • 98
5 votes
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Root Locus and Routh–Hurwitz stability criterion

Suppose we have a third order polynomial in the form : $$ s^3+a_2s^2+a_1s+a_0 = 0$$ There is nice caveat for third order systems which is derived from the Routh-Hurwitz stability criterion. In order ...
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5 votes
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Can someone explain how the output of this control system is derived?

Well as a fresh start: net(n) is the value before the node, this can be seen by equation (1). The value after the node is the following (lets call this $x$ for simplicity): $$x(n) = net(n) - a_1x(n-1) ...
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  • 1,079
5 votes
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How do I interpret the following Bode, Nyquist and Nichols diagrams?

Your systems shows extremely close pole-zero cancellation. So much even that it nearly removes 4 poles and zeros. Lets look at why, starting with the Bode plot: The magnitude plot is constantly ...
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  • 1,079
5 votes

Full state feedback of a closed loop system

Let me phrase this a bit more elaborate. Suppose we have a state space system, ie: $$\dot{x} = Ax + Bu$$ Where the dynamics of the system are presented through $A$. For instance, the poles of the ...
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  • 1,079
4 votes

What is the best method to model the input of an electro-mechanical system for control design and simulations?

There are various levels of plant models you can develop, depending on what you want to do. The model you mention is probably suitable for most of the cases in terms of designing a controller. However,...
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  • 1,806
4 votes
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Steady state value, a possible shortcut?

Think for a moment about what it means for $\eta(t)$ to have reached its steady state. It means precisely that $\dot{\eta}(t)=0$. If you plug that into your first equation and solve for $\eta(t)$ ...
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4 votes
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Control theory - Differential equations and state variable description

A professor of mine, long ago, once quipped: "Give me a word... any word at all... and I'll show you how the root of that word is a PDE!" A touch of Philosophy All physical systems are modeled ...
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