PID Controller and Tuning Flashcards
(36 cards)
What is a P controller?
It is essentially an amplifier with an adjustable gain
What happens if we adjust Kp?
it will adjust the rise time and steady state error. This can be unwanted in higher order systems as it can give unwanted oscillation.
What is the equation for a PI controller?
Kp + Ki / s
What is the type number of a PI controller?
Type 1
What is the steady state error of a PI controller to a Step Input?
0 because it is a type 1 system.
Why does a PI controller have the potential to be less stable?
Because it increases the order of the system.
What is the equation for a PD controller?
Kp + Kds.
What does the derivative term add to the system?
It adds damping.
What effect does damping have on the system?
It can reduce overshoot and rise time along with stabilise an unstable system.
Why is a PD controller hard to implement in real life?
Noise.
What is the equation for a PID controller?
Kds^2 + Kps + Ki / s
What is the effect on the rise time, overshoot, settling time and steady state error of the system if we increase Kp?
Rise Time: decrease
Overshoot: increase
Settling Time: small change
Steady State Error: decrease
What is the effect on the rise time, overshoot, settling time and steady state error of the system if we increase Ki?
Rise Time: decrease
Overshoot: increase
Settling Time: increase
Steady State Error: ELIMINATES
What is the effect on the rise time, overshoot, settling time and steady state error of the system if we increase Kd?
Rise Time: small change
Overshoot: decrease
Settling Time: decrease
Steady State Error: small change
What is good about the Ziegler Nichols Tuning Method?
We don’t need to know the model of the system.
What is the transport delay in the Ziegler Nichols Method?
It is the time taken for the signal provided to be acted upon ( the time taken to see a change in the system ).
What is a model of the Open Loop ZN tuning method?
G(s) = Ke^-Td*s / Tau * s + 1
What is the Open Loop ZN model similar to?
What effect does multiplying by the exponential have?
The time constant form for a first order system.
Multiplying by the exponential moves everything to the right.
What is the ZN gain Kp for a P controller?
Tau / K * Td
What are the ZN gains Kp and KI for a PI controller?
Kp = 0.9 * Tau / KTd Ki = 0.27 * Tau / KTd^2
What are the gains for the ZN PID controller?
Kp = 1.2Tau / KTd Ki = 0.6Tau / KTd^2 Kd = 0.6Tau / KTd
What are the necessary conditions to use the open loop tuning method?
The system must be stable and have an S shape with delay.
For the ZN closed loop tuning method, what must the state of the system be?
It can be stable or unstable, it doesn’t matter since we don’t need a model of the system.
How do we apply the ZN closed loop tuning method?
Start with just P control. Increase the gain until we get sustained oscillations. This means that it is marginally stable. We record this gain as the ULTIMATE GAIN (Ku). We take the period of Oscillation (Tu) as the ULTIMATE PERIOD. From these two values we can work out any P, PI, or PID controller gains.
