Pwm 3g529

Presenter: Val Tocitu

 Introduction and definitions  Types of PWM  Methods of generation  Characteristics of PWM  Applications and examples  Implementation on the HCS12

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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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Definitions Duty Cycle: on-time / period Vlow is often zero

VAVG  DVHI  (1  D)VLOW

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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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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

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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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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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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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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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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 10/29/2009

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Disadvantages of PWM Cost Complexity of circuit Radio Frequency Interference Voltage spikes Electromagnetic noise

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Presenter: Jason Kulpe

 Introduction and definitions  Types of PWM  Methods of generation  Characteristics of PWM  Applications and examples  Implementation on the HCS12

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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

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PWM used with D/A conversion • commonly used in toys • low 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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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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Frequency of the PWM Upper Limits Lower Limits Signal 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

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Example: PWM with 555 Timer Potentiometer is used to adjust the duty cycle

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Example: Specifying circuit elements

Requirements 1. Maxon EC-16 brushless motor, Time constant = 8.75 ms 1  8.5 ms  f

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

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Example: Specifying circuit elements This circuit has a PWM frequency according to:

1.44 f  R1C1 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 10/29/2009

Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

f

≥ 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

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Where can I buy a PWM controller? Texas Instruments Digikey Mo Electronics Critical Velocity Motor Control

BIGGER

SMAL L

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 Pulse Width Modulation - Val Tocitu, $55.95 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

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PWM Implementation The signal is outputted

through Port P Six Channels Dedicated Chip

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PWM Module Each channel has a

dedicated counter Programmable duty and period Independently adjustable clock, polarity, and alignment

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PWM Module- Other Features 8-bit and 16-bit resolution ed 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

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PWM Configuration Configured through

specific s s are located from $00E0 to $00FE There are repeated s (ex. 0013-0017)

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PWM Enable

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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PWM Polarity

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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PWM Clock Select

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

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PWM Prescaler

 Located at $00E3  Variable: PWMPRCLK  Used to prescale clocks A and B

Bus Clock Frequency  Resolution    PWM Frequency Bus Clock Frequency  N (2  1)   PWM Frequency

Presclarer 

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PWM Scale A 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 

Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

Clock A Frequency 2  PWMSCLA

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PWM Scale B 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 

Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

Clock B Frequency 2  PWMSCLB

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PWM Center Align

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

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Signal Alignment  Signal changes when counter

is equal to period  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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PWM Control  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

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PWM Counter 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

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PWM Period  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

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Left-Aligned: PWMPERx 

PWM Source Frequency PWM Signal Frequency

Center-Aligned: PWM Source Frequency PWMPERx  2  PWM Signal Frequency

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PWM Duty • • • •

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 Duty Cycle  PWMPERx 100 Duty Cycle  PWMPERx Polarity = 1: PWMDTYx  100

Polarity = 0: PWMDTYx  PWMPERx 10/29/2009

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PWM Shutdown • • • • • • •

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 U 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 45 • PWM5INL: Determines active level of pin 5

How it all works Clock A, SA, B, or SB

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Example 8 106 Prescaler  8  3.91  4  PWMPRCLK  $02 (2  1)  8 103

Desired Signal:  8 kHz PWM signal  Duty Cycle of 30%  Left Aligned  Channel 1  Low → High  8-bit channel





 8 10 6    4 2 10 6   PWMPER1    250  $FA 8 103 8 103

PWMDTY1  250 -

30  250  175  $AF 100

PWMCLK  $00

PWMCAE  $00 PWMPOL  $00 PWMCTL  $00 PWME  $02

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Assembly Code PWME EQU PWMPOL EQU PWMCLK EQU PWMPRCLK PWMCAE PWMCTL EQU PWMPER1 PWMDTY1 ORG LDAA STAA STAA STAA STAA LDAA STAA LDAA STAA LDAA STAA STAA …… 10/29/2009

$00E0 $00E1 $00E2 EQU EQU $00E5 EQU EQU

$00E3 $00E4 $00F3 $00F9

$1000 #$00 PWMCLK ; Sets source clocks to clock A PWMPOL ; The signal goes from low to high PWMCTL ; Makes all channels 8-bit PWMCAE ; Signals are left aligned #$FA PWMPER1 ; Sets the period to 250 clock cycles #$AF PWMDTY1 ; Makes the duty cycle equal to 30% #$02 PWMPRCLK ; Sets the prescaler to 4 PMWE ; Enables and starts channel 1 48

C Code

#include /* 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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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)

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Questions?

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