Transcript Slide 1
ME 4447/6405 October 29 th , 2009 By: Val Tocitu Jason Kulpe Alexandre Mariuzza
Presenter: Val Tocitu
Introduction and definitions Types of PWM Methods of generation Characteristics of PWM Applications and examples Implementation on the HCS12
Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 10/29/2009 2
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 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 3
Definitions
Duty Cycle: on-time / period V low is often zero
V AVG
DV HI
( 1
D
)
V LOW
10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 4
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 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 5
Types of Pulse Width
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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 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 10/29/2009 7
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 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 8
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 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 11
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 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 10/29/2009 12
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 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 13
Motor Control Diagrams
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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 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 10/29/2009 15
Disadvantages of PWM
Cost Complexity of circuit Radio Frequency Interference Voltage spikes Electromagnetic noise 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 16
Presenter: Jason Kulpe
Introduction and definitions Types of PWM Methods of generation Characteristics of PWM Applications and examples Implementation on the HCS12
Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 10/29/2009 17
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 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 18
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 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 19
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 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 20
Frequency of the PWM Signal
Lower Limits Upper Limits 1. Must be at least 10 times higher than the control system frequency 2. Higher than 20kHz – audible frequency of sounds to avoid annoying sound disturbances, caused by magnetostriction 3. If too low the motor is pulsed, not continuous, because the motor’s inductance can not maintain the current 4. Inverse of frequency should be much less than the motor/load time constant 5. Higher error from ripple voltages 10/29/2009 1. If too high the inductance of the motor causes the current drawn to be unstable 2. MOSFET transistor generates heat during switching 3. Limited by resolution of controller 4. Eddy currents generated in electromagnetic coils which lead to adverse heating 5. Heat losses in electromagnetic materials is proportional to frequency squared Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 22
Example: PWM with 555 Timer
Potentiometer is used to adjust the duty cycle 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 23
Example: Specifying circuit elements Requirements
1. Maxon EC-16 brushless motor, Time constant = 8.75 ms
f
1 8 .
5
ms
f
117 Hz 2. Want to avoid audible frequencies
f ≥
20 kHz 3. PID control loop running at 150 Hz
f ≥
10 ∙ 150 Hz 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 24
Example: Specifying circuit elements
This circuit has a PWM frequency according to:
f
1 .
44
R
1
C
1 Set
f
to 25 kHz to add in a factor of safety Choosing
C 1
to be 100 nF,
R 1
is 576 Ω ~ 500 Ω Recalculating with these values
f
= 28.8 kHz 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza
f
Check constraints
≥ 117 Hz ≥ 20 kHz ≥ 1.5 kHz 25
Matlab can do PWM!
The procedure works similar to the generation of analog PWM using a sinusoid and saw-tooth wave 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 26
Where can I buy a PWM controller?
Texas Instruments Digikey Mouser Electronics Critical Velocity Motor Control
SMALL
Texas Instruments TAS5508B 8-Channel Digital Audio PWM Processor 64 pin chip, max 192 kHz frequency $7.25
10/29/2009 18 kHz frequency Continuous 28 amps $55.95
Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 120 amps, used for hybrid vehicles $469.00
H U G E
27
Presenter: Alex Mariuzza
Introduction and definitions Types of PWM Methods of generation Characteristics of PWM Applications and examples Implementation on the HCS12
Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 10/29/2009 28
PWM Implementation
The signal is outputted through Port P Six Channels Dedicated Chip 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 29
PWM Module
Each channel has a dedicated counter Programmable duty and period Independently adjustable clock, polarity, and alignment 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 30
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 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 10/29/2009 31
PWM Configuration
Configured through specific registers Registers are located from $00E0 to $00FE There are repeated registers (ex. 0013-0017) 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 32
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 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 33
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 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 34
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 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 35
PWM Prescaler Register
Located at $00E3 Variable: PWMPRCLK Used to prescale clocks A and B Presclarer Bus Clock Resolution Frequency PWM Frequency 10/29/2009 ( 2
N
Bus 1 ) Clock Frequency PWM Frequency Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 36
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 10/29/2009 Clock SA Frequency Clock A Frequency 2 PWMSCLA Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 37
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 10/29/2009 Clock SB Frequency Clock B Frequency 2 PWMSCLB Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 38
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 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 39
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 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 10/29/2009 40
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 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 41
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 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 42
PWM Period Register
Located at $00F2 through $00F7 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: PWMPERx PWM Source Frequency PWM Signal Frequency Center-Aligned: PWMPERx PWM Source Frequency 2 PWM Signal Frequency 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 43
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 • 10/29/2009 Channel is disabled Polarity = 0: Polarity = 1: PWMDTYx PWMDTYx PWMPERx Duty Cycle Duty Cycle PWMPERx PWMPERx 100 100 44
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 45
How it all works
Clock A, SA, B, or SB 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 46
Example
Desired Signal: 8 kHz PWM signal Duty Cycle of 30% Left Aligned Channel 1 Low → High 8-bit channel Prescaler ( 2 8 8 1 ) 10 6 8 10 3 3 .
91 4 PWMPRCLK $02 PWMPER1 8 10 6 4 8 10 3 2 8 10 10 3 6 250 $ FA PWMDTY1 250 30 250 100 175 $ AF PWMCLK $00 PWMCAE $00 PWMPOL $00 PWMCTL $00 PWME $02 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 47 10/29/2009
Assembly Code
PWME PWMPOL PWMCLK PWMPRCLK PWMCAE PWMCTL PWMPER1 PWMDTY1 EQU EQU EQU EQU EQU EQU EQU EQU $00E0 $00E1 $00E2 $00E3 $00E4 $00E5 $00F3 $00F9 10/29/2009 ORG LDAA STAA STAA STAA STAA LDAA STAA LDAA STAA LDAA STAA STAA …… $1000 #$00 PWMCLK PWMPOL PWMCTL PWMCAE #$FA PWMPER1 #$AF PWMDTY1 #$02 PWMPRCLK PMWE ; Sets source clocks to clock A ; The signal goes from low to high ; Makes all channels 8-bit ; Signals are left aligned ; Sets the period to 250 clock cycles ; Makes the duty cycle equal to 30% ; Sets the prescaler to 4 ; Enables and starts channel 1 48
C Code
#include
10/29/2009 // Signals are left aligned // Sets the period of the signal to 250 clock // Makes the duty cycle equal to 30% //Sets the prescaler to 4 //Enables and starts channel 1 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 49
REFERENCES
http://en.wikipedia.org/wiki/Pulse-width_modulation http://www.netrino.com/Embedded-Systems/How-To/PWM-Pulse-Width-Modulation Cetinkunt, Sabri.
Mechatronics
. Hoboken, NJ: Wiley, 2006. Print.
http://www.jimfranklin.info/microchipdatasheets/00538c.pdf
http://www.allaboutcircuits.com/vol_6/chpt_6/9.html
http://www.dprg.org/tutorials/2005-11a/index.html
http://www.4qdtec.com/pwm-01.html
http://skywalker.cochise.edu/rgill/ch02elec.ppt
http://pcbheaven.com/wikipages/PWM_Modulation/ Matlab 2009 online documentation http://www.epanorama.net/links/motorcontrol.html#ac MC9S12C Family, MC9S12GC Family Reference Manual, (pp. 347-382) Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 10/29/2009 50
Questions?
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