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Basic Control Action By :- Vishal Thakur 100104143 B.Tech (EE) Sem V Section B
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Introduction• A controller compares the actual value of output with the reference input, determines the deviation, and produces a control signal that will reduce the deviation to zero or to a small value.• The manner in which the controller produces the control signal is called the control action.
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Block Diagram of a BasicIndustrial Control System
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• Actuating signal is proportional to error signal• Such a system always has a steady-state error in the step response. Such a steady- state error is called an offset.
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Change in gain in P controller • Increase in gain: → Upgrade both steady-state and transient responses →Increases oscillations → Reduce steady-state error → Reduce stability!
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Integral Controller• Integral of error with a constant gain → increase the system type by 1 →eliminate steady-state error for a unit step input → amplify overshoot and oscillations
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Proportional-Plus-Integral Control• To eliminate offset, the proportional controller may be replaced by a proportional-plus-integral controller.• If integral control action is added to the controller, then, as long as there is an error signal, a signal is developed by the controller to reduce this error, provided the control system is a stable one.
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Change in gain for PI controller • Increase in gain: → Do not upgrade steady-state responses → Increase slightly settling time → Reduces stability and bandwidth of system → Increase oscillations and overshoot!
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Derivative Controller• Differentiation of error with a constant gain → detect rapid change in output → reduce overshoot and oscillation→ do not affect the steady-state response
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Proportional-Plus-Derivative ControlWith derivative action, the controller output is proportional tothe rate of change of the measurement or error.
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Effect of change for gain PD controller • Increase in gain: → Upgrade transient response → Decrease the peak and rise time → Improves stability and bandwidth of system → Increase overshoot and settling time!
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Proportional-Plus-Derivative -Plus-Integral Control• A proportional–integral–derivative controller (PID controller) is a control loop feedback mechanism widely used in industrial control systems – a PID is the most commonly used feedback controller.• A PID controller calculates an "error" value as the difference between a measured process variable and a desired setpoint. The controller attempts to minimize the error by adjusting the process control inputs.
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• The PID controller calculation involves three separate constant parameters, and is accordingly sometimes called three-term control: the proportional, the integral and derivative values, denoted P, I, and D.• These values can be interpreted in terms of time: P depends on the present error, I on the accumulation of past errors, and D is a prediction of future errors, based on current rate of change.
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