1. Pulse Width Modulation
ME 4447/6405
October 29th, 2009
By:
Val Tocitu
Jason Kulpe
Alexandre Mariuzza

2. Introduction and definitions Types of PWM Methods of generation
Presenter: Val Tocitu
Introduction and definitions
Types of PWM
Methods of generation
Characteristics of PWM
Applications and examples
Implementation on the HCS12
10/29/2009
Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

3. What is it?
Output signal alternates between on and off within specified period
Controls power received by a device
The voltage seen by the load is directly proportional to the source voltage
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

4. Definitions Duty Cycle: on-time / period Vlow is often zero
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

5. Types of Pulse Width Pulse center fixed, edges modulated
Leading edge fixed, tailing edge modulated
Tailing edge fixed, leading edge modulated
Pulse Width constant, period modulated
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

6. Types of Pulse Width
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

7. Analog Generation of PWM
Analog PWM signals can be made by combining a
saw- tooth waveform and a sinusoid
PWM output is formed by the intersection of the saw-tooth wave and sinusoid
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

8. Digital Methods of Generating PWM
Digital: Counter used to handle transition
Delta : used to find the PWM at a certain limit
Delta Sigma: used to find the PWM but has advantage of reducing optimization noise
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

9. Delta Method Output signal compared with limits
Every time limits reached, changes state
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

10. Delta Sigma Method PWM signal generated by Delta method
Error = output – reference
Error integrated
State changes when integration reaches limits
Advantage
Circuit simpler
Reduces quantization
noise by high pass filter
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

11. Applications to DC Motors
The voltage supplied to a DC motor is proportional to the duty cycle
Both brushed and brushless motors can be used with PWM
Both analog and digital control techniques and components are available
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

12. Three Phase AC motors with PWM
3 different AC currents at different phases
Phase: 120 degrees apart
Creates constant power transfer
Rotating magnetic field
Pulses substitute for AC current
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

13. Space Vector Modulation
Used for three-phase AC motors
Convert DC current to AC current
Gates turned on/off at different intervals
3 PWM created
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

14. Motor Control Diagrams
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15. Advantages of PWM average value proportional to duty cycle, D
low power used in transistors used to switch the signal
fast switching possible due to MOSFETS and power transistors at speeds in excess of 100 kHz
digital signal is resistant to noise
less heat dissipated versus using resistors for intermediate voltage values
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

16. Disadvantages of PWM Cost Complexity of circuit
Radio Frequency Interference
Voltage spikes
Electromagnetic noise
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

17. Introduction and definitions Types of PWM Methods of generation
Presenter: Jason Kulpe
Introduction and definitions
Types of PWM
Methods of generation
Characteristics of PWM
Applications and examples
Implementation on the HCS12
10/29/2009
Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

18. Applications of PWM
In the past, motors were controlled at intermediate speed by using resistors to lower delivered power
Electric stove heater
Lamp dimmers
Voltage regulation – convert 12 volts to 5 volts by having a 41.7% duty cycle
Sound production: PWM controlled signals give sound effects similar to a chorus
Power transfer: PWM used to reduce the total power given to a load without relying on resistive losses
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

19. PWM used with D/A conversion
commonly used in toys
lowpass filter smooths out transients from harmonic effects
frequency values of harmonics doesn’t change, but the amplitude does, which adjusts the analog output signal
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

20. PWM used to transmit data in telecommunications
clock signal is found “inside” PWM signal
more resistant to noise effects than binary data alone
effective at data transmission over long distance transmission lines
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

21. Concerns: Ripple of PWM Signal
Ripple is the noise in the output signal
Appropriate PWM controllers can minimize these effects
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

22. Frequency of the PWM Signal
Lower Limits
Upper Limits
Must be at least 10 times higher than the control system frequency
Higher than 20kHz – audible frequency of sounds to avoid annoying sound disturbances, caused by magnetostriction
If too low the motor is pulsed, not continuous, because the motor’s inductance can not maintain the current
Inverse of frequency should be much less than the motor/load time constant
Higher error from ripple voltages
If too high the inductance of the motor causes the current drawn to be unstable
MOSFET transistor generates heat during switching
Limited by resolution of controller
Eddy currents generated in electromagnetic coils which lead to adverse heating
Heat losses in electromagnetic materials is proportional to frequency squared
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

23. Example: PWM with 555 Timer
Potentiometer is used to adjust the duty cycle
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

24. Example: Specifying circuit elements
Requirements
Maxon EC-16 brushless motor,
Time constant = 8.75 ms
2. Want to avoid audible frequencies
f ≥ 20 kHz
3. PID control loop running at 150 Hz
f ≥ 10 ∙ 150 Hz
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

25. f Example: Specifying circuit elements ≥ 117 Hz ≥ 20 kHz ≥ 1.5 kHz
This circuit has a PWM frequency according to:
Check constraints
Set f to 25 kHz to add in a factor of safety
Choosing C1 to be 100 nF, R1 is 576 Ω ~ 500 Ω
Recalculating with these values f = 28.8 kHz
≥ 117 Hz
≥ 20 kHz
≥ 1.5 kHz f
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

26. Matlab can do PWM!
The procedure works similar to the generation of analog PWM using a sinusoid and saw-tooth wave
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

27. HUGE Where can I buy a PWM controller? BIGGER Texas Instruments
Digikey
Mouser Electronics
Critical Velocity Motor Control
HUGE
BIGGER
SMALL
Texas Instruments TAS5508B
8-Channel Digital Audio PWM Processor
64 pin chip, max 192 kHz frequency
$7.25
18 kHz frequency
Continuous 28 amps
$55.95
120 amps, used for hybrid vehicles
$469.00
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Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

28. Introduction and definitions Types of PWM Methods of generation
Presenter: Alex Mariuzza
Introduction and definitions
Types of PWM
Methods of generation
Characteristics of PWM
Applications and examples
Implementation on the HCS12
10/29/2009
Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

29. PWM Implementation The signal is outputted through Port P Six Channels
Dedicated Chip
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30. PWM Module Each channel has a dedicated counter
Programmable duty and period
Independently adjustable clock, polarity, and alignment
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31. PWM Module- Other Features
8-bit and 16-bit resolution supported
Two PWM channels can be concatenated together
Four source clocks (A, SA, B, SB)
Emergency Shutdown
Some changes take a complete cycle to be implemented
Modes of Operation:
Normal: everything is available
Wait: Low-power consumption and clock disabled
Freeze: Option to disable clock is available
Emergency Shutdown- can be triggered with input from pin 5 of Port P
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32. PWM Configuration Configured through specific registers
Registers are located from $00E0 to $00FE
There are repeated registers (ex )
There are 30 registers, lots of them are repeated
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33. PWM Enable Register Located at $00E0 Code Warrior variable: PWME
Set PWMEx to 0 to disable the channel
Set PWMEx to 1 to enable it
Channel is activated when bit is set
If 16-bit resolution used, then PWME4/2/0 are deactivated
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34. PWM Polarity Register Located at $00E1 Code Warrior variable : PWMPOL
Set PPOLx to 0, signal goes from low to high
Set PPOLx to 1, signal goes from high to low
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35. PWM Clock Select Register
Located at $00E2
Code Warrior variable : PWMCLK
Set PCLK5/4/1/0 to 0 to use clock A
Set PCLK5/4/1/0 to 1 to use clock SA
Set PCLK3/2 to 0 to use clock B
Set PCLK3/2 to 1 to use clock SB
Clock A and B are independent prescaled clocks
Clock SA and SA are based on clocks A and B
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36. PWM Prescaler Register
Located at $00E3
Variable: PWMPRCLK
Used to prescale clocks A and B
Clock A and B are independent prescaled clocks
Clock SA and SA are based on clocks A and B
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37. PWM Scale A Register Located at $00E8 Code Warrior variable: PWMSCLA
Store a hexadecimal value in order to change the clock frequency of SA
Note: if set to $00, PWMSCLA is set to 256
Clock A and B are independent prescaled clocks
Clock SA and SA are based on clocks A and B
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38. PWM Scale B Register Located at $00E9 Code Warrior variable: PWMSCLB
Store a hexadecimal value in order to change the clock frequency of SA
Note: if set to $00, PWMSCLB is set to 256
Clock A and B are independent prescaled clocks
Clock SA and SA are based on clocks A and B
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39. PWM Center Align Register
Located at $00E4
Code Warrior variable: PWMCAE
Set CAEx to 0 for left align signal
Set CAEx to 1 for center align signal
Note: can only be set when channel is disabled
Clock A and B are independent prescaled clocks
Clock SA and SA are based on clocks A and B
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40. Signal Alignment
Signal changes when counter is equal to period register
In the center aligned mode, the PWM counter goes from a down-count to a up-count to down-count, etc.
In the left aligned mode, the PWM counter is a up-counter and rests to zero when it overflows
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41. PWM Control Register Located at $00E5 Code Warrior variable: PWMCTL
Set CONxy to 0 to keep PWM channels separate (8-bit)
Set CONxy to 1 to concatenate PWM channels x and y together (16-bit).
Channel y determines the configuration
x becomes the high byte and y becomes the low byte
Bits PSWAI and PFRZ set either wait or freeze mode
Changes only occur when channels are disabled
Clock A and B are independent prescaled clocks
Clock SA and SA are based on clocks A and B
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42. PWM Counter Register Located at $00EC through $00F1
Code Warrior variable: PWMCNTx
One per channel
It tracks the cycle counts
It can be read
If written to, the count is reset to $00 and a up-count starts
Clock A and B are independent prescaled clocks
Clock SA and SA are based on clocks A and B
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43. PWM Period Register Located at $00F2 through $00F7 Left-Aligned:
Variable: PWMPERx
Store a hexadecimal value to limit maximum value of counter
Changes occur when:
Current period ends
Counter is written to
Channel is disabled
Left-Aligned:
Clock A and B are independent prescaled clocks
Clock SA and SA are based on clocks A and B
Center-Aligned:
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44. PWM Duty Register Located at $00F8 through $00FD
Code Warrior variable: PWMDTYx
Store a hexadecimal value to control when signal changes
Changes occur when:
Current period ends
Counter written to
Channel is disabled
Polarity 0- counts low time
Polarity 1- counts high time
Polarity = 0:
Polarity = 1:
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45. PWM Shutdown Register Located at $00FE Code Warrior variable: PWMSDN
PWMENA: Enables and disables emergency shut down
PWMIF (Interrupt flag): Set when an input is detected in pin 5
PWMIE (Interrupt Enable): Enables and disables CPU interrupts
PWMRSTRT: Resets the counters
PWMLVL (Shutdown Output Level): Determines if output is high or low when shutdown
PWM5IN (Input Status): Reflects status of pin 5
PWM5INL: Determines active level of pin 5
Polarity 0- counts high time
Polarity 1- counts low time 45 45

46. How it all works
Clock A, SA, B, or SB
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47. Example Desired Signal: 8 kHz PWM signal Duty Cycle of 30%
Left Aligned
Channel 1
Low → High
8-bit channel
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48. Assembly Code PWME EQU $00E0 PWMPOL EQU $00E1 PWMCLK EQU $00E2
PWMPRCLK EQU $00E3
PWMCAE EQU $00E4
PWMCTL EQU $00E5
PWMPER1 EQU $00F3
PWMDTY1 EQU $00F9
ORG $1000
LDAA #$00
STAA PWMCLK ; Sets source clocks to clock A
STAA PWMPOL ; The signal goes from low to high
STAA PWMCTL ; Makes all channels 8-bit
STAA PWMCAE ; Signals are left aligned
LDAA #$FA
STAA PWMPER1 ; Sets the period to 250 clock cycles
LDAA #$AF
STAA PWMDTY1 ; Makes the duty cycle equal to 30%
LDAA #$02
STAA PWMPRCLK ; Sets the prescaler to 4
STAA PMWE ; Enables and starts channel 1 ……
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49. C Code #include <hidef.h> /* common defines and macros */
#include <mc9s12c32.h> /* derivative information */
#pragma LINK_INFO DERIVATIVE “mc9s12c32”
// Set up chip in expanded mode
MISC = 0x03;
PEAR = 0x0C;
MODE = 0xE2;
//Set up PWM Registrer
PWMCLK = 0; // Sets source clocks to clock A
PWMPOL = 0; // The signal goes from low to high
PWMCTL = 0; // Makes all channels 8-bit
PWMCAE = 0; // Signals are left aligned
PWMPER1 = 250; // Sets the period of the signal to 250 clock
PWMDTY1 = 175; // Makes the duty cycle equal to 30%
PWMPRCLK = 2; //Sets the prescaler to 4
PMWE = 2; //Enables and starts channel 1 ….
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50. REFERENCES http://en.wikipedia.org/wiki/Pulse-width_modulation
Cetinkunt, Sabri. Mechatronics. Hoboken, NJ: Wiley, Print.
Matlab 2009 online documentation
MC9S12C Family, MC9S12GC Family Reference Manual, (pp )
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51. Questions?
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