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TMS320F28062F: Current limit and ISR consistency lost

Noah Erickson
Prodigy 170 points
Part Number: TMS320F28062F
Other Parts Discussed in Thread: MOTORWARE

Hi E2E,

I am bringing up a new board design and am encountering an interesting issue using a TMS320F28062F with Motorware lab11a. I currently have my user motor max current limit set to 3A just to get things up and running which works extremely well at times. I have been monitoring the time and consistency of mainISR with a debug pin set high at the start and set low at the end of the function and have seen some inconsistency and am wondering where this is coming from. Below is a scope capture of the erratic mainISR behavior along with the loss of current control. Also shown is our PWM signals, phase current and phase voltage.

Some other information that may be of value is we are running at 15kHz PWM with USER_NUM_CTRL_TICKS_PER_SPEED_TICK and USER_NUM_CTRL_TICKS_PER_TRAJ_TICK set to 15 to match PWM frequency. USER_NUM_PWM_TICKS_PER_ISR_TICK, USER_NUM_ISR_TICKS_PER_CTRL_TICK, USER_NUM_CTRL_TICKS_PER_CURRENT_TICK and USER_NUM_CTRL_TICKS_PER_EST_TICK are all set to 1.

Does anyone have any insight into why my Main isr is so inconsistent? 

Regards,

Noah

  • 0
    Prodigy 170 points
    Hi E2E,

    I wanted to follow up with an update on how I got around this issue. I ended up bypassing the speed control loop and setting an Iq reference for the current control loop. After the motor reached a certain RPM threshold I switch back over to speed control. This gives a steady current limit on ramp up and I have not seen any main ISR misfires since.

    Unfortunately I never discovered the root cause of the issue.

    Regards,

    Noah
  • 0 in reply to Noah Erickson
    TI__Genius 17175 points
    Can you scope the CPU clock and PWM clock frequency to ensure they are correct? Perhaps you have overflowed ISR during speed control and that is what has been causing the inconsistency.

    Sean
  • 0 in reply to Sean Bigley
    Prodigy 170 points
    Hi Sean,

    I had to put this project on hold but should be able to get a scope capture of that in a week or so. I definitely want to figure out what is going on here and I will post an update.

    I am curious what overflowing the ISR would look like? If I have a PWM frequency of 15kHz would that just mean my ISR is taking longer than the 66us period? I ask because I believe I have a bit of overhead, roughly 20us of downtime.

    Thanks,

    Noah