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TMS320F28069M: Running FOC on four motors in sync.

Prabhjot Singh1
Intellectual 505 points
Part Number: TMS320F28069M
Other Parts Discussed in Thread: CDCM9102

Can I use two F28069M controllers to run 4 FOCs on four motors in a synced manner? By sync I mean that 4 FOCs should start at same time for all the motors and all 6X4=24 PWMs should be synced with same Time base .

If it is possible then how to achieve it? Will there be a need for a common clock for the two microcontrollers?

  • 0
    Intellectual 480 points
    I find hard to synchronize motors down to the clock cycle using sensorless technology. If you do need absolute synchronization you might want to consider position feedback (resolver or hall effect sensors, depending on the accuracy needed). For instaSPIN, even if you synchronize the PWM pulses among all the boards, the motor will still react differently depending on many variables in the system. By the way, for instaSPIN the motor starts in open loop - it is hard to predict how each motor will start and eventually get up to speed.
  • 0 in reply to Armando Barbedo
    Intellectual 505 points

    Can I get an idea about how to achieve synchronization of the two microcontrollers. What I think is I have to provide one external oscillator output to two microcontrollers. Am I correct or is there a better way? I understand there would be different responses by motors because of their different characteristics and initial states. But the first requirement is to achieve synchronization. Later issues can be resolved by deploying position sensors or HF current injection.

  • 0 in reply to Prabhjot Singh1
    Intellectual 480 points
    I would share the clocks (use a clock generator such as CDCM9102), share the reset pin, and keep the power supply very tight between the micros. Additionally I would create an interrupt based on an external event (GPIO) to synchronize the code, since the micro startup time may or may not be deterministic.

    I will be adamant in saying that the synchronization of the micros is a drop in the bucket compared with the variability of the motors. If this is for a vehicle (guess based on the 4 motors) you will have to keep a super tight control of the motor speeds.

    Best of luck!