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Recent content by cswilson

  1. cswilson

    VFD with 'partial' support for PM motors

    If you are driving a PM motor with a VFD with no feedback of any kind, you are basically treating it as a big stepper motor in microstepping mode. As you suspect, overload would cause a catastrophic failure - not just loss of torque, but rapidly alternating torque tending to bring the motor to...
  2. cswilson

    VFD in a lathe application

    Some vector drives will keep the "magnetization current" active even when there is no request for orthogonal "torque current". This way, when there is a request for torque current, there is not the delay in getting the rotor to magnetize. One of the trickiest things about "sensorless"...
  3. cswilson

    Inverter Drive Setting

    The "VC" in 1 and 2 stands for "vector control". This is closed-loop control of the motor as opposed to the open-loop V/F (voltage/frequency) control of 3. As to the first letter, different companies use different terminology. "S" is probably for "Space" as "Space Vector Control" is a term...
  4. cswilson

    How does sensorless field oriented control algorithms (induction motor) regulate slip?

    In the standard operating range of induction motors, torque and slip frequency have an approximately linear relationship. In open-loop control -- DOL or V/Hz -- as the load torque varies, the speed, and so the slip frequency will change until the generated torque balances the load torque. In...
  5. cswilson

    Earth Spinning Faster

    About a decade ago, I stumbled on this issue. I spent some time on it, but was too busy to go into depth. There is a very tight relationship between these "length-of-day" variations and certain components of "atmospheric angular momentum". It appears that a lot of the variation has to do with...
  6. cswilson

    N-1 Reliability Criteria for HVDC - Symmetrical Monopole VSC

    A few years ago, I got a great tour of the southern end of the Pacific Intertie HVDC line in Los Angeles, which typically brings power from the big dams on the Columbia River south to the big population centers. The thing I found most interesting was how they handle the loss of one of a pair...
  7. cswilson

    Stepper motor acceleration

    We have many customers who output microstepping pulse trains at over 1 MHz. It's not unusual at all. Of course, you need to check what the maximum frequency your drive can accept is, and make sure your pulse width is short enough that you actually have distinct pulses at the higher frequencies.
  8. cswilson

    Stepper motor acceleration

    "Is there really much difference between a brushless servo motor and a stepper motor other than the controller?" Not really. Both are AC synchronous motors. You are correct that the real difference is in the control. We have multiple customers who buy standard stepper motors, add an encoder on...
  9. cswilson

    Stepper motor acceleration

    The dynamics of stepper motor torque generation are those of a lightly damped spring. Imagine pulling impulsively on a wheeled cart using a Slinky. This diagram shows the lightly damped response of a stepper motor to full-step commands (left). If you issue a subsequent step command increment...
  10. cswilson

    Servo motor inertia ratio

    There's probably been more nonsense offered about "inertial matching" issues than any other in all the years I have been in servo control. There is really nothing "optimal" about a 1:1 ratio. In the real world, what you typically need to worry about most is how your resonant and anti-resonant...
  11. cswilson

    Remember the "Fixed" Can Opener Bridge?

    The roads along the Charles River between Boston and Cambridge -- Storrow Drive on the Boston side and Memorial Drive on the Cambridge size -- have underpasses with less than 10-foot clearance. These roads pass by major universities -- Boston University, MIT, and Harvard. Of course, move-in and...
  12. cswilson

    Delta Tau GPH1020000 PWM Geo Drive 480VAC

    I'm afraid the information given to you is true. As an old product, near obsolescence, it is build-to-order and not a stocked product. I have looked to see if we have any "off the record" parts, but no luck so far. Curt Wilson Omron Delta Tau
  13. cswilson

    Regenerative brake

    Bill: You've done exactly the transformations I recommend to people trying to understand field-oriented control of induction motors. I almost put these in my last comment, but didn't have the time. I would go one step further and express the slip in Hz as well as RPM. The next step is to...
  14. cswilson

    Regenerative brake

    Bill: With an induction motor, any time you use negative slip (electrical frequency less than mechanical frequency), the motor becomes a generator. With a synchronous motor, any time you use a negative torque angle (electrical angle lagging mechanical angle), the motor becomes a generator. So...
  15. cswilson

    Regenerative brake

    Perusing a Tesla forum, I see that Tesla cars have a warning light that comes on at low outside temperatures, telling you that the regenerative braking capability is reduced. This is due to the reduction in charging rate of the battery at lower temperatures.
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