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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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PID controller - IntroP

I

D

+ -

Amp Outputprocess

Vset

Vsensor

Verror Vout

Sensor

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Term Math Function Effect 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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P amplifier• Rout=1 ohm• PM is 87• Close loop: BW=19K.

2

1

20

2

R K

R K

2

1

RH sR

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D amplifier

Lowers the gain in high frequency and help stabilize the amplifier

1 1R C sH s

R C s

Main conflicts:

• Stability of the block.

• Functionality of the block

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D amplifier

1 1R C sH s

R C s

• PM=87• Close loop BW = 200[Hz]

1

12.5

100

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R K

R

C F

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I amplifierCancel the affect of bias voltage

Cancels affect of bias currents

' 11 '

RH sR 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

' 11 '

RH sR R C s

' 2.5

125

125

8x

R M

R K

R K

C F

• PM=20

• Close loop BW 8m[Hz]

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Summing amplifier• Rin=Ri• PM is 87• Close loop BW=17K.

1 2 31 2 3

1 1 1out FV R V V V

R R R

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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+0.1In=1

Timer=0In=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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Q&A

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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/