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TECHNION - ISRAEL INSTITUTE OF TECHNOLOGY
Department of Electrical EngineeringControl and Robotics Lab
Design a digitally controlled analog PID controller
Designer: Idan Yahav
Supervisor: David Gidony
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PID controller - Intro• The PID controller helps get your output where you
want it, with minimal overshoot, and with little error.
• PID stands for: P -Proportional, I - Integral, D - Derivative. We apply this functions on the error signal.
• Verror is the difference between where you want to go (Vset), and where you're actually at (Vsensor).
• Verror = Vset - Vsensor.
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TermMath
FunctionEffect on Control System
PProportional
KP x Verror
Typically the main drive in a control loop, KP reduces a large part of the overall error.
IIntegral
KI x ∫ Verror
dt
Reduces the final error in a system. Summing even a small error over time produces a drive signal large enough to move the system toward a smaller error.
DDerivative
KD x dVerror /
dt
Counteracts the KP and KI terms when the output changes quickly. This helps reduce overshoot and ringing. It has no effect on final error.
PID controller - Intro• The controller performs the PID mathematical
functions on the error and applies their sum to a process
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GoalMain goal : To design a digital controlled PID controller.
Part A - Analog• Design the analog amplifiers PID and summing.
Part B – digital:• Design a microcontroller that will control an LCD
screen and a variable gain element.
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Chosen Architecture
• Amplifiers supply ±15[V].• Digital supplier 5 ]V[.• Red arrows indicate digital potentiometer.
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Part A : analog design• Spec:
• Input signal is 0.1 [V]
• Functionality BW- 10m-200 [Hz]
• Issues
• Feedback amplifiers : stability check.
• Rout and Rin of the P and summing amplifiers.
• Check the synergy between the blocks.
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D amplifier
Lowers the gain in high frequency and help stabilize the amplifier
1 1
R C sH s
R C s
Main conflicts:
• Stability of the block.
• Functionality of the block
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I amplifierCancel the affect of bias voltage
Cancels affect of bias currents
' 1
1 '
RH s
R R C s
Main conflicts:
• Stability of the block.
• Functionality of the block
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I amplifierCancel the affect of bias voltage
Cancels affect of bias currents
' 1
1 '
RH s
R R C s
' 2.5
125
125
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x
R M
R K
R K
C F
• PM=20
• Close loop BW 8m[Hz]
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Part B : Digital Design• The microcontroller is like a small computer.• It includes a CPU, memory and I/Os.
In order to design the digital solution we need:• C code (with a CCS compiler).• Interrupts. (do not return to the start of main)• Timers.• Datasheets.
Part B : Digital Design• For a single press: count = count ± 0.1 (depend on
the button that was pressed).
• For a long press: count = count ± 0.9 the first time and count = count ± 1 on the rest.
• If count >10 :count=count-10.
Flow chart
1616
Stop timer
Start timer
Count+0.1
In=1Timer=0
In=1Timer=1
In=0Timer=x
Start timer
Count+1
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Part B : Digital Design• A function that writes to the screen was
implemented
• 2 denounce solution were implemented
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Opens and Next steps• Stabilize the integrator.• Design a power supply: ±15 [V], gnd, 5[V] and an
adjustable voltage down to -5 [V].• Implement a code for the digital potentiometer.• Design protection blocks for the card.• Calibration solution.• Design a printed card.• Measurements on the card.
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References• http://en.wikipedia.org/wiki/Microcontroller• http://en.wikipedia.org/wiki/Switch• http://electronics.stackexchange.com/questions/22209/calc
ulating-resistor-and-capacitor-values-for-an-op-amp-differentiator-circuit-d
http://www.ecircuitcenter.com/circuits/opdfr/opdfr.htmhttp://www.ecircuitcenter.com/circuits/opdfr_OL/opdfr_open_loop.htm
• http://www.ecircuitcenter.com/circuits/pid1/pid1.htm • http://circuitalley.phpnet.us/circuit4.html• http://www.underwar.co.il/14-IT-Security/d318/