PID Control & ACS550 and ACH550

PID in every day life Cruise function in a car: User sets the speed (Input = SetPoint = Reference) Car measures (Feedback = Actual) Car automatically minimizes the error (Deviation) between these two (Input and Feedback) ”…as a result is a smooth ride.”

PID: General Widely used in automation and process industries. Applications: Motor Speed Control Pressure & Temperature Control Flow Control (Water) Level Control

PID: General Proportional-integral-derivative (PID) controller. Control loop feedback method: VSD (controller) compares the reference signal (input) to the actual signal (feedback) and controls the speed of the drive according to the difference (error) of these signals.

PID: General PID algorithm includes three different variables: P(roportional): Proportional reaction to the error of the reference and measured signals: improves the rise time! I(ntegral): Determines the accumumulated proportional offset over time: eliminates the steady state error! D(erivative): Anticipated control: determines the slope of the error signal. Reduces the overshoot of the integral component.

PID: General The output (v) of the PID controller: P I D

Increasing variable’s value PID: General Effects of controllers (P, I, D): When increasing the value of the variables… CLOSE LOOP RESPONSE Increasing variable’s value RISE TIME OVERSHOOT SETTLING TIME STEADY-STATE ERROR Kp Decreases Increases Small Change KI Eliminates KD Decrease None Remember that the variables are dependent on each other and thus by changing one value you might effect on the others! The table above is only a good reference! ! ! (Table @ http://www.engin.umich.edu/group/ctm/PID/PID.html)

PID: Tuning Traditional Ziegler-Nichols method: Pure P controller (disable D and I) Increase the gain untill the system oscillates (critical gain KC) Read the oscillation period Tc Calculate the values according to the table below: Controller P I D P 0.5KC PI 0.4KC 0.8TC PID 0.6KC 0.5TC 0.125TC

PID: General Control type by application: Level Control: Usually P Flow & Pressure & Temperature Control: PI Motor Speed Control: PID (Figures @ http://www.engin.umich.edu/group/ctm/PID/PID.html)

PID: General Using PID can be served: SMOOTH AND FAST SYSTEM!!! Fast response/rise time No overshoot Low steady-state error SMOOTH AND FAST SYSTEM!!!

PID: General Sometimes all three controllers are not needed to obtain a good response! Depending on the system a good enough control can be achieved by using only PI controller! Always keep the system as simple as possible!

PID: ACS550 PID functions available both on ACS550 and ACH550 ACS550: PID control Groups: 40 (Process PID SET 1) 41 (Process PID SET 2) and 42 (EXT / TRIM PID) Pre-defined PID control macro: Set 9902 PID Assistant

PID: ACS550 PID control macro: (9902)

PID: ACH550 ACH550: PID controller is in every HVAC macro. Groups: 40 (Process PID SET 1) 41 (Process PID SET 2) and 42 (EXT / TRIM PID) Macro selections: Set 9902 PID Assistant

PID: ACS550 and ACH550 ACS550 and ACH550 schematic of reference signal using parameter group 40: In order to use PID controller, parameter 1106 must set to EXT2 (19).

PID: ACS550 and ACH550 Parameters 4001-4009: Used to adjust the PID: Param. 4001: GAIN Param. 4002: INTEGRATION TIME Param. 4003: DERIVATION TIME …

PID: ACS550 and ACH550 Rule of thumb in parameter setting: PID GAIN (parameter 4001) increase until the system starts to oscillate right value is half of this PID INTEG TIME (parameter 4002) decrease until the system starts to oscillate right value is 2*Ti

PID: Summary What is it for the customer?! Accurate: Quality of the Process and Goods Easiness: (PID Macro) Time Savings Extent in Use: Compatibility Maintenance & Support