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Steady-State Analysis

Contents. IntroductionSteady-State Error for Unity Feedback SystemStatic Error Constants and System TypeSteady-State Error for Non-Unity Feedback Systems. Introduction. Steady-state error, ess: The difference between the input and the output for a prescribed test input as time, t approaches 8.. Step Input.

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Steady-State Analysis

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    1. Steady-State Analysis

    2. Contents Introduction Steady-State Error for Unity Feedback System Static Error Constants and System Type Steady-State Error for Non-Unity Feedback Systems

    3. Introduction Steady-state error, ess: The difference between the input and the output for a prescribed test input as time, t approaches 8.

    4. Introduction Steady-state error, ess: The difference between the input and the output for a prescribed test input as time, t approaches 8.

    5. Test Inputs Test Inputs: Used for steady-state error analysis and design. Step Input: Represent a constant position. Useful in determining the ability of the control system to position itself with respect to a stationary target. Ramp Input: Represent constant velocity input to a position control system by their linearly increasing amplitude. Parabolic Input: Represent constant acceleration inputs to position control. Used to represent accelerating targets.

    6. Test Inputs

    7. Unity Feedback Systems To determine the steady-state error, we apply the Final Value Theorem: The following system has an open-loop gain, G(s) and a unity feedback since H(s) is 1. Thus to find E(s), Substituting the (2) into (1) yields,

    8. Unity Feedback Systems By applying the Final Value Theorem, we have: This allows the steady-state error to be determined for a given test input, R(s) and the transfer function, G(s) of the system.

    9. Unity Feedback Systems For a unit step input: The term: The dc gain of the forward transfer function, as the frequency variable, s approaches zero. To have zero steady-state error,

    10. Unity Feedback Systems For a unit ramp input: To have zero steady-state error, If there are no integration in the forward path: Then, the steady state error will be infinite.

    11. Unity Feedback Systems For a unit parabolic input: To have zero steady-state error, If there are one or no integration in the forward path: Then, the steady state error will be infinite.

    12. Unity Feedback Systems Example: Find the steady-state errors for inputs of 5u(t), 5tu(t), and 5t2u(t).

    13. System Type System Type: The value of n in the denominator or, the number of pure integrations in the forward path. Therefore, If n = 0, system is Type 0 If n = 1, system is Type 1 If n = 2, system is Type 2

    14. System Type Example: Problem: Determine the system type.

    15. Static Error Constant Static Error Constants: Limits that determine the steady-state errors. Position constant: Velocity constant: Acceleration constant:

    16. Position Error Constant, Kp Steady-state error for step function input, R(s): Position error constant: Thus,

    17. Velocity Error Constant, Kv Steady-state error for step function input, R(s): Position error constant: Thus,

    18. Acceleration Error Constant, Ka Steady-state error for step function input, R(s): Position error constant: Thus,

    19. Static Error Constant & System Type Relationships between input, system type, static error constants, and steady-state errors:

    20. Analysis via static error constant Example: Find the steady-state errors for inputs of 5u(t), 5tu(t), and 5t2u(t) by first evaluating the static error constants.

    21. Non-Unity Feedback Systems Example: Calculate the error constants and determine ess for a unit step, ramp and parabolic functions response of the following system.

    22. Non-Unity Feedback Systems Example: Calculate the error constants and determine ess for a unit step, ramp and parabolic functions response of the following system. For step input,

    23. Non-Unity Feedback Systems Example: Calculate the error constants and determine ess for a unit step, ramp and parabolic functions response of the following system. For ramp input,

    24. Non-Unity Feedback Systems Example: Calculate the error constants and determine ess for a unit step, ramp and parabolic functions response of the following system. For parabolic input,

    25. Non-Unity Feedback Systems Problem: Calculate the error constants and determine ess for a unit step, ramp and parabolic functions response of the following system.

    26. Further Reading… Chapter 5 Dorf R.C., Bishop R.H. (2001). Modern Control Systems (9th Ed), Prentice Hall. Chapter 7 Nise N.S. (2004). Control System Engineering (4th Ed), John Wiley & Sons.

    27. The End… "A scientist can discover a new star, but he cannot make one. He would have to ask an engineer to do that…"

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