SteadyState Error

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Questions and Answers

What is the equation for the steady-state error for ramp inputs of unit velocity?

$e_{\infty} = \lim_{s\to 0} G(s)$

$e_{\infty} = \lim_{s\to 0} s^2G(s)$

$e_{\infty} = \lim_{s\to 0} 1/G(s)$

$e_{\infty} = \lim_{s\to 0} sG(s)$ (correct)

What does the system type represent?

The number of feedback loops in the system

The gain of the system

The number of pure differentiations in the forward path

The number of pure integrations in the forward path (correct)

What is the significance of static error constants in control systems?

They determine the transient response of the system

They specify the number of feedback loops in the system

They are the steady-state error specifications for control systems (correct)

They indicate the stability of the system

How does increasing system gain affect the steady-state error?

Increasing system gain decreases the steady-state error Signup and view all the answers

In a unity feedback system, the steady-state error is best expressed in terms of which transfer function?

Open-loop transfer function $G(s)$ Signup and view all the answers

Which criterion is used for the verification of stability in the closed-loop system?

Routh-Hurwitz criterion Signup and view all the answers

What type of signal is used to establish specifications for a control system’s steady-state error characteristics?

Ramp signal Signup and view all the answers

What is a requirement for achieving zero steady-state error?

At least one pure integration in the forward path Signup and view all the answers

What type of inputs can be used to evaluate a system's ability to follow linearly increasing, constant-velocity, and constant-acceleration inputs?

Step, ramp, and parabolic inputs Signup and view all the answers

Which type of systems is the discussion on steady-state errors limited to?

Stable systems Signup and view all the answers

What must be checked during steady-state error analysis and design to avoid erroneously applying expressions derived for calculating steady-state error?

Stability Signup and view all the answers

For which type of systems can a system with an integrator in the forward path have zero error in the steady state for a step input?

Unity feedback systems Signup and view all the answers

What is the impact of increasing the dc gain of G1(s) in reducing the steady-state error due to a step disturbance?

It reduces the steady-state error due to a step disturbance Signup and view all the answers

How does the system type relate to the steady-state error?

System type is defined based on the number of pure integrations and affects the steady-state error Signup and view all the answers

How are the static error constants related to the steady-state error?

The static error constants appear in the denominator of the steady-state error equations and affect the steady-state error Signup and view all the answers

How is the steady-state error with a disturbance included expressed mathematically?

The steady-state error with a disturbance included involves the transform of the output and the disturbance Signup and view all the answers

What are the three main specifications focused on in control systems analysis and design?

Transient response, stability, steady-state errors Signup and view all the answers

In steady-state error analysis, what is the steady-state error defined as?

Difference between the input and the output for a prescribed test input as $t \rightarrow \infty$ Signup and view all the answers

Which chapter revisits the concepts of transient analysis for higher-order systems?

Chapter 8 Signup and view all the answers

What happens to forced responses if the system is unstable?

They are overpowered by natural responses that increase without bound Signup and view all the answers

Study Notes

Control System Steady-State Error and Disturbance Rejection

The steady-state error for a step input, u(t), is determined by the limits of the three terms in the denominator, known as static error constants: position constant (Kp), velocity constant (Kv), and acceleration constant (Ka).
The static error constants depend on the form of G(s) and can take values of zero, finite constant, or infinity, affecting the steady-state error as they appear in the denominator of the steady-state error equations.
System type is defined based on the number of pure integrations in the forward path, denoted by 'n' in the denominator, with Type 0, Type 1, and Type 2 systems corresponding to n 0, n 1, and n 2, respectively.
Table 7.2 links steady-state error, static error constants, and system type, showing their values as functions of input waveform and system type.
Static error constants, such as position constant (Kp), velocity constant (Kv), and acceleration constant (Ka), can be used to specify the steady-state error characteristics of control systems.
Feedback control systems can be designed to follow the input with small or zero error, compensating for disturbances or unwanted inputs entering the system.
The expression for steady-state error with a disturbance included involves the transform of the output, given by Cs EsG1sG2s DsG2s, and the steady-state value of the error can be found using the final value theorem.
The steady-state error due to a step disturbance can be reduced by increasing the dc gain of G1(s) or decreasing the dc gain of G2(s).
Figure 7.12 illustrates that minimizing the steady-state value of the error requires either increasing the dc gain of G1(s) or decreasing the dc value of G2(s).
Control systems often do not have unity feedback, with the feedback path having a pure gain other than unity or some dynamic representation.
A general nonunity feedback system differs from a unity feedback system, as the error is not the difference between the input and the output, and the signal at the output of the summing junction is called the actuating signal.
The feedback system's structure, including input transducer, controller, plant, and feedback, impacts the system's performance and its ability to reject disturbances.

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Description

Explore concepts related to steady-state error in control systems, including static error constants, system type, and disturbance rejection. Understand how feedback control systems can be designed to minimize error and compensate for disturbances.