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InstaSPIN High speed limit

Nigel MacDonald
Prodigy 55 points
Other Parts Discussed in Thread: MOTORWARE, INSTASPIN-BLDC, TMS320F28069M

What is the highest electrical rpm InstaSPIN can support? We need to control a motor between 10K electrical rpm and 200K electrical rpm (5-100Krpm, 4 pole). The examples I've seen so far are at much lower speeds.

 

  • 0
    TI__Guru** 119600 points

    We have controlled motors up to about 2.5-3KHz electrical with the FAST algorith and InstaSPIN-FOC with 15 or 20 KHz control loop rates (FAST can run at the same speed or even rates of /2, /3, /4).  To do any closed loop control a general rule is you need to be updating at least 7 times per electrical cycle (and 10x is preferred). So 3KHz would be 21 KHz control loop (and 10x would be 30 KHz).  In a classical FOC system you also need to compensate for the difference in the rotor angle when you sample (estimate) to when you output your command. This is included in InstaSPIN-FOC starting with the latest MotorWare version _09. 

    I believe  InstaSPIN-BLDC has been used at even higher frequencies as you aren't trying to orient the precise position of the stator field but rather just need to commutate "close enough". But you still need to keep the 7-10x rule.

     

  • 0 in reply to ChrisClearman
    Prodigy 30 points
    Hello Chris,
    Adding to this relatively old question, have you found that the Piccolo processor (TMS320F28069M) and InstaSPIN-FOC would still be a viable solution at 3kHz? Or do you feel that it is necessary to move to a Delfino processor? If you feel that moving to Delfino is required, is the main advantage the faster clock speed, or is there some other advantage?

    I completely agree that running at 10x fundamental is needed. So 30kHz for the control loop. The software appears to allow the PWM frequency to be higher, so 60Khz, or 90kHz is possible. Do you find that with 60kHz or 90kHz that the 90MHz clock of the TMS320F28069M provides sufficient number of bits of resolution in the PWM, or does InstaSPIN use the high resolution PWM feature?
  • 0 in reply to Chris Brune
    TI__Guru** 119600 points
    I think it's border line viable in a real system once you add in your own system code, comms, etc.
    If you limit your inner loops to about 24 KHz you may have enough spare bandwidth for everything.

    It also depends on the current if an FOC technique is really appropriate. Some of these very large short circuit current motors with ridiculously low inductances just make it so difficult to get good current measurements. And if the data in is bad the control loop output will be bad.

    We don't use the HRPWM feature in InstaSPIN. It may provide some benefit on very low duty cycles, but in general it doesn't buy you much in motor control.