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Pulse Width Modulation

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

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

  2. 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

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

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

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

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

  10. 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

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

  12. Motor Control Diagrams Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

  13. 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

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

  15. 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

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

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

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

  19. Frequency of the PWM Signal Upper Limits Lower 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 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

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

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

  22. Example: Specifying circuit elements This circuit has a PWM frequency according to: Check constraints Set f to 25 kHz to add in a factor of safety Choosing C1to 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 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

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

  24. Where can I buy a PWM controller? 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 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza

  25. 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

  26. 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

  27. 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

  28. 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 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 31

  29. 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

  30. 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

  31. 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

  32. 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

  33. PWM Prescaler Register Located at $00E3 Variable: PWMPRCLK Used to prescale clocks A and B 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 36

  34. 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 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 37

  35. 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 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 38

  36. 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

  37. 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 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 40

  38. 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

  39. 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

  40. 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: Center-Aligned: 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 43

  41. 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: Polarity = 1: 10/29/2009 44

  42. 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

  43. How it all works Clock A, SA, B, or SB 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 46

  44. Example • Desired Signal: • 8 kHz PWM signal • Duty Cycle of 30% • Left Aligned • Channel 1 • Low → High • 8-bit channel 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 47

  45. 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 …… 10/29/2009 48

  46. 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 …. 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 49

  47. 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

  48. Questions? 10/29/2009 Pulse Width Modulation - Val Tocitu, Jason Kulpe, Alex Mariuzza 51

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