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PWM clocks in 2xPM_Sensorless

Lucifer Angel
Intellectual 995 points

Other Parts Discussed in Thread: CONTROLSUITE

When PWM init section looks like this:

 

// Initialize PWM module

pwm1.PeriodMax = SYSTEM_FREQUENCY*1000000*T/2;

pwm2.PeriodMax = SYSTEM_FREQUENCY*1000000*T/2;

PWM_INIT_MACRO(pwm1)  

PWM_INIT_MACRO(pwm2)

 

But if, for instance, so:

 

// Initialize PWM module

pwm1.PeriodMax = SYSTEM_FREQUENCY*1000000*T/2;

pwm2.PeriodMax = SYSTEM_FREQUENCY*500000*T/2;

PWM_INIT_MACRO(pwm1)

PWM_INIT_MACRO(pwm2)

 

... Then the motor wich is on the pwm1 gets vibrating and moving slower.

What' s the problem?

 

  • 0
    TI__Mastermind 43730 points

    What do you mean by motor on PWM1 ?

     

    For three phase PM motor you need all there PWM1, 2 and 3, this is what this example 2xPMSensorless demonstrates,

     

    regards

    Manish Bhardwaj

  • 0 in reply to Manish Bhardwaj
    Intellectual 995 points

    Thanks, Manish.

    Then thats what should be clarified.

    I meant not PWM1 & PWM2 but pwm1 and pwm2 - software instances for PWM 1A, PWM 1B, PWM 2A, PWM 2B and PWM 3A, PWM 3B, PWM 4A, PWM 4B respectively.

    Lines 211 through 216 and 1568 through 1589 of the original 2xPM_Sensorless.c can give You an idea, suppose.

    Thanks again.

  • 0 in reply to Lucifer Angel
    TI__Mastermind 43730 points

    Lucifer,

    In your two instances you have halfed the switching frequency of the inverter controlling the motor, This implied instead of 10Khz you now operate at  5kHz. 

    This reduces the bandwidth your controller has. Depending on the system you are trying to control and how the frequency response of the system is this would affect the control operation and that's what you are seeing.

    I am assuming that you are using the motors that ship with the kit.

    regards

    Manish Bhardwaj

  • 0 in reply to Manish Bhardwaj
    Intellectual 995 points

    Thanks again, Manish.

    1. Yes, I just want PWM period of the second motor (on pwm2) to be higher than that of the first ... and this really implies operation at 20 kHz instead of 10 kHz.

    2. Vibrations only occur when PWM periods are different on two motors - when they're equal it's okay.

    Regards anyway.

  • 0 in reply to Lucifer Angel
    TI__Mastermind 43730 points

    Lucifer apologies for all the confusion,

    Few things i wanted to check

    1. What version of 2xPM Sensorless are you using? CCSv4 or CCSv3? Are you using the LVMultiAxis+PfcKit_v1.4\2xPM_Sensorless ?

    The way the project is configured a single interrupt is used for both the motors, Now as your second motor is spinning at 20Khz now the control is not cycle by cycle for the second motor.

    Which motor vibrates the one with the higher switching frequency or the lower frequency?

     

  • 0 in reply to Manish Bhardwaj
    Intellectual 995 points

    1. 2xPM_Sensorless from latest ControlSUITE and CCSv4 : LVMultiAxis+PfcKit_v1.4\2xPM_Sensorless

    The one with slower PWM vibrates. On the faster PWM there is no motor at all.

    Manish Bhardwaj said:

    The way the project is configured a single interrupt is used for both the motors, Now as your second motor is spinning at 20Khz now the control is not cycle by cycle for the second motor.

    Ah, yes, I see. Maybe noise from faster PWM switching circuit causes motor to vibrate?

    Thank You very much, Manish.

     

  • 0 in reply to Lucifer Angel
    Intellectual 995 points

    Oops...

    Can someone clarify the matter?

    Thanks in advance.