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What criteria can be used to study the stability of linear systems?
What criteria can be used to study the stability of linear systems?
- Bode Stability Criterion
- Routh-Hurwitz Criterion (correct)
- Nyquist Stability Criterion
- Lyapunov's Method
What defines a stable system?
What defines a stable system?
- Unbounded output for an unbounded input
- Bounded output for an unbounded input
- Bounded output for a bounded input (correct)
- Unbounded output for a bounded input
Which type of system is stable for all ranges of component values?
Which type of system is stable for all ranges of component values?
- Absolutely stable system (correct)
- Dynamically stable system
- Conditionally stable system
- Marginally stable system
How can PID controller parameters be related to a controlled system's response?
How can PID controller parameters be related to a controlled system's response?
What is true about an open-loop control system's absolute stability?
What is true about an open-loop control system's absolute stability?
Which of the following methods can be used for PID tuning?
Which of the following methods can be used for PID tuning?
What type of system allows for stability only under certain conditions?
What type of system allows for stability only under certain conditions?
What is the characteristic of the response of a stable first-order control system to a unit step input?
What is the characteristic of the response of a stable first-order control system to a unit step input?
What defines a conditionally stable system?
What defines a conditionally stable system?
How can a marginally stable system be characterized?
How can a marginally stable system be characterized?
What is a necessary condition according to the Routh-Hurwitz Stability Criterion?
What is a necessary condition according to the Routh-Hurwitz Stability Criterion?
What can be inferred if a control system does not satisfy the necessary condition for stability?
What can be inferred if a control system does not satisfy the necessary condition for stability?
For which values of K is the given system stable: $s^4 + s^3 + s^2 + s + K = 0$?
For which values of K is the given system stable: $s^4 + s^3 + s^2 + s + K = 0$?
In the context of Routh-Hurwitz stability, what does the sufficient condition determine?
In the context of Routh-Hurwitz stability, what does the sufficient condition determine?
What is the damping ratio required for the closed loop roots when the gain has to be set?
What is the damping ratio required for the closed loop roots when the gain has to be set?
What is the nature of a system with roots on the imaginary axis?
What is the nature of a system with roots on the imaginary axis?
What characteristic does the nth order characteristic equation need to maintain?
What characteristic does the nth order characteristic equation need to maintain?
What type of compensation is mentioned for control systems?
What type of compensation is mentioned for control systems?
What indicates that a closed loop control system is marginally stable?
What indicates that a closed loop control system is marginally stable?
What can be inferred about the roots of the characteristic equation if a control system is stable?
What can be inferred about the roots of the characteristic equation if a control system is stable?
In a negative feedback system, what is the function of the open loop transfer function?
In a negative feedback system, what is the function of the open loop transfer function?
What gain value could lead to overshoot approximately equal to 5% in a speed control system?
What gain value could lead to overshoot approximately equal to 5% in a speed control system?
Which factor primarily dictates the stability of a control system?
Which factor primarily dictates the stability of a control system?
What is indicated by the characteristic polynomial's coefficients in a stability analysis?
What is indicated by the characteristic polynomial's coefficients in a stability analysis?
What is the sufficient condition for Routh-Hurwitz stability?
What is the sufficient condition for Routh-Hurwitz stability?
In the example given, what is the characteristic polynomial being analyzed for stability?
In the example given, what is the characteristic polynomial being analyzed for stability?
What must be true about the coefficients of the characteristic polynomial for it to satisfy the necessary condition of stability?
What must be true about the coefficients of the characteristic polynomial for it to satisfy the necessary condition of stability?
For the polynomial $s^3 + 2s^2 + 4s + K = 0$, what range of $K$ values will ensure system stability?
For the polynomial $s^3 + 2s^2 + 4s + K = 0$, what range of $K$ values will ensure system stability?
What is the consequence of having a sign change in the first column of the Routh array?
What is the consequence of having a sign change in the first column of the Routh array?
In creating a Routh array, what does the first column represent?
In creating a Routh array, what does the first column represent?
During the Routh array formation, the expression for $b_1$ is derived from which elements?
During the Routh array formation, the expression for $b_1$ is derived from which elements?
What does the element $c_1$ represent in the Routh array for stability analysis?
What does the element $c_1$ represent in the Routh array for stability analysis?
What is the primary purpose of a compensator in a control system?
What is the primary purpose of a compensator in a control system?
In a Bode diagram, which graph expresses the phase shift of the system response?
In a Bode diagram, which graph expresses the phase shift of the system response?
The expression $T(j heta) = \frac{10}{j\omega + 10}$ is an example of what type of system?
The expression $T(j heta) = \frac{10}{j\omega + 10}$ is an example of what type of system?
When the frequency $ heta$ is much greater than 10, what does $T(j heta)$ approach in decibels?
When the frequency $ heta$ is much greater than 10, what does $T(j heta)$ approach in decibels?
What will be the phase shift $ heta$ when $ heta$ is much less than 10?
What will be the phase shift $ heta$ when $ heta$ is much less than 10?
What is the purpose of the grid in a Bode plot?
What is the purpose of the grid in a Bode plot?
What is the result of applying the Routh-Hurwitz criterion to a characteristic equation with all positive coefficients?
What is the result of applying the Routh-Hurwitz criterion to a characteristic equation with all positive coefficients?
What characterizes a second order transfer function?
What characterizes a second order transfer function?
When representing a second order system, what do the variables $ heta_n$ and $ extit{zeta}$ signify?
When representing a second order system, what do the variables $ heta_n$ and $ extit{zeta}$ signify?
In the expression for phase shift derived from $T(j\omega)$, what does $ an^{-1}$ indicate?
In the expression for phase shift derived from $T(j\omega)$, what does $ an^{-1}$ indicate?
How is the Bode magnitude calculated for a basic system?
How is the Bode magnitude calculated for a basic system?
What implication does a Bode plot display when the magnitude approaches -3 dB?
What implication does a Bode plot display when the magnitude approaches -3 dB?
What is indicated by the characteristic equation $s^3 + 2s^2 + s + 1 = 0$ having all positive coefficients?
What is indicated by the characteristic equation $s^3 + 2s^2 + s + 1 = 0$ having all positive coefficients?
In frequency response analysis, what is the term 'frequency response' fundamentally describing?
In frequency response analysis, what is the term 'frequency response' fundamentally describing?
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Study Notes
Stability
- Stability is a crucial characteristic of systems, determining if their output remains controlled for any given input.
- A stable system produces a bounded output for a given bounded input, ensuring predictable behavior.
- An unstable system's output can grow uncontrollably, even for a bounded input, leading to unpredictable and potentially dangerous behavior.
Types of Systems based on Stability
- Absolutely Stable System: Stable for the entire range of component values.
- Conditionally Stable System: Stable only for a particular range of component values.
- Marginally Stable System: Stable with a constant amplitude and frequency of oscillations for a bounded input.
Stability Analysis
- Routh-Hurwitz Stability Criterion: A powerful tool for analyzing the stability of linear systems.
- Necessary Condition: All coefficients of the characteristic polynomial must be positive. This indicates all roots of the equation have negative real parts.
- Sufficient Condition: All elements in the first column of the Routh array should have the same sign. This guarantees system stability.
- Routh Array Method: A systematic process to form the Routh array for the given characteristic polynomial.
Example 1: Determining Stability
- The characteristic polynomial is: s^4 + 3s^3 + 4s^2 +2s +1 = 0
- Satisfies the necessary condition as all coefficients are positive.
- Forms the Routh array:
- s^4: 1 4 1
- s^3: 3 2 0
- s^2: 10/3 1 0
- s^1: 1.1 0 0
- s^0: 1 0 0
- Satisfies the sufficient condition as all elements in the first column are positive.
- Therefore, the system is stable based on the Routh-Hurwitz criterion.
Example 2: Determining Stability Based on K Values
- The characteristic polynomial is: s^3 + 2s^2 + 4s + K = 0
- Forms the Routh array:
- s^3: 1 4
- s^2: 2 K
- s^1: (8-K)/2 0
- s^0: K 0
- For a stable system, all elements in the first column must be positive.
- Therefore, the system is stable when 0 < K < 8
Example 3: Determining Stability Based on K Value
- The characteristic polynomial is: s^4 + s^3 + s^2 + s + K = 0
- Forms the Routh array:
- s^ 4: 1 1 K
- s^3: 1 1 0
- s^2: 0 K 0
- s^1: -infinity 0 0
- s^0: K 0 0
- The system becomes unstable for any value of K greater than zero due to the sign change in the first column's elements after s^2.
Example 4: Determining the Gain for Unstable System
- The system's structure involves a feedback loop with an open-loop transfer function.
- The gain at which the system becomes unstable can be calculated using the characteristic equation for the closed-loop system.
Example 5: Determining Gain for Specific Damping Ratios
- The open-loop transfer function is given: K(s+2)/(s(s-1))
- The gain (K) can be determined for specific damping ratios by analyzing the closed-loop system's characteristic equation and its roots.
- Damping ratio information can be used to calculate the gain (K) that results in that specific damping ratio (e.g., 0.707 for critically damped).
Example 6: Determining Stability Based on Kp and KD
- The stability of a feedback system with proportional (Kp) and derivative (KD) controllers can be analyzed based on the characteristic equation of the closed-loop system.
- The range of Kp and KD values leading to stability can be defined using the Routh-Hurwitz criterion.
Bode Diagram
- A Bode diagram is a graphical representation of a system's frequency response, used to analyze and predict control system stability.
- It consists of two graphs:
- Bode Magnitude Diagram: Plots the magnitude response in decibels against frequency.
- Bode Phase Diagram: Plots the phase shift in degrees against frequency.
- Bode plots help determine the system's stability based on the frequency response characteristics, identifying gain and phase margins.
Creating Bode Plots
- Bode plots are used to visualize the frequency response of a system, particularly in dynamic systems.
- Bode(T): This command in MATLAB generates a Bode plot for a SISO dynamic system represented by 'T', where 'T' is the transfer function of the system.
- Example: Using MATLAB, a Bode plot can be created for the system: T = tf(10, [1 10]);
- The plots show the system's behavior at different frequencies, revealing key characteristics like resonance points and stability margins.
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