What is a compensator?
A component that is inserted into a control system to compensate for a deficient performance.
What are the pros and cons of a open-loop system
(3, 3)?
pros:
- simple
-easy to maintain
- stable
cons:
- inaccurate
-unreliable
- changes from disturbances cannot be corrected
What are some drawbacks with simple closed-loop controller and how can you fix it?
Oscillations in outputs which can be overcome using a more complex controller like a PID controller.
What are the important closed-loop system terminologies (8) ?
- Process Variable: the parameter being controlled
- Sensor: used to measure and provide feedback
- The Set Point: the desired value for the process variable, like the desired temperature of a case
- Error: the different between the process variable and the set point
-rise time: time to go from 100% to 90% of the final value - overshoot: the maximum amount about the final value
- settling time: time to settle within a certain percentage of the final value
- steady-state error: the difference between the process variable and the target
What is a PID controller?
a device that applies a correction based on Proportional, integral and derivative terms. it simplifies the sum of three parallel actions to generate a control output.
What are the advantages of using a PID controller (4)?
- accurate
- eliminates steady-state error
- reduce overshoot and oscillations
- widely applicable
What is a proportional controller?
provides a control input that is proportional to the error value
What are the advantages of proportional controller(3)?
- simplicity
- fast response
- stabilization
What are the limitations of the proportional controller(2)?
- steady-state error
- oscillations
What is a proportional integral controller?
a feedback controller combining proportional and integral actions to correct errors in a system.
What are the features of a PI controller(2)?
P: reacts to the current error.
I: reacts to the accumulation of past errors
What does Integral control do?
eliminates the effect of disturbance at steady-state
What are the advantages of proportional integral controller(3)?
- simplicity
- no steady-state error
- tracking
What are the limitations of proportional integral controller(2)?
- slow response
- oscillations
Important things to know about applying PI controllers (2)?
- pi controller needs tuning to eliminate steady-state error
- choosing low and high values for proportional and integral gains cause weak performance or instability
What is derivative control (3)?
- proportional to the rate of change of the error signal
- introduces an element of prediction into the control action
- has a damping effect and reduces the oscillations caused by a large gain Kp and improves settling time.
What are the affects of introduction a derivative control gain KD (3)?
- increase stability
- reduce overshoot
- improve the transient response
What the uses cases for P, PI and PID?
P: when speed is more important the accuracy
PI: when steady-state accuracy is important
PID: high performance systems requiring stability
What are the 5 steps to designing a PID controller?
- obtain an open-loop response and determine what needs to be improved
- add a proportional control to improve the rise time
- add an integral control to eliminate steady-state error
- if needed, add a derivative control to improve the overshoot.
- adjust kp, ki, and kd until you obtain a desired overall response.
