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Is it possible to apply the so called scalar control or V/f control which is used for ACIM control also for PMSM control?

I think no because of V/f control used for ACIM does not know current position of the PMSM rotor and due to this fact does not know position of the rotor magnetic field.

Due to this fact stator magnetic field produced by three phase voltage source inverter is not in the appropriate position in respect to the rotor magnetic field. Is my idea correct?

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Permanent magnet synchronous motors were driven by v/f control before vector control was invented. Variable frequency drives were developed with encouragement from synthetic fiber industry manufacturers who had been using variable pitch belt driven frequency changers to drive speed-matched PMSMs in the process that produced the fibers. The loads did not change very much during operation. The frequency was carefully ramped up to accelerate the load.

In addition to tuning the acceleration and deceleration rates to suit the load, it is necessary to have an instantaneous over-current trip function to protect the VFD. Most VFDs on the market today have a v/f control mode available along with the acceleration and over-current trip functions. It should be ok to use v/f control without worrying about damaging the motor.

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  • \$\begingroup\$ Thank you for your reaction. I am going to use V/f control of PMSM in following scenario. Ramp up the unloaded motor to nominal frequency and then applied nominal torque to its shaft. I am afraid of the transient after loading the motor. \$\endgroup\$ – Steve Jan 17 at 15:07
  • \$\begingroup\$ If you are planning to load the motor with a mechanical clutch, I would recommend an induction motor with a vector control. \$\endgroup\$ – Charles Cowie Jan 17 at 15:20
  • \$\begingroup\$ may I ask you for looking at my question link \$\endgroup\$ – Steve Feb 14 at 10:47
  • \$\begingroup\$ I looked at it. I can not help with that. \$\endgroup\$ – Charles Cowie Feb 14 at 14:19
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Yes, it's possible to drive a permanent magnet synchronous motor blindly with just plain V/f control. Stepper motors are commonly used like that. Most steppers are basically two-phase PMSMs that are designed for being driven open loop.

However, such a scheme would be very inefficient (and would probably burn up a motor not designed for it). The current required to spin a given load scales linearly with the load torque. Since you'd have no feedback, you'd have to deliver enough current all the time to overcome the worst possible load. Also, if the load overpowers the motor torque for even an instant, loss of sync between the rotor and the stator magnetic field will occur, usually stopping the motor unexpectedly.

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  • \$\begingroup\$ Thank you for your reaction. I am also afraid of permanently demagnetizing the permanent magnets of the motor. Because lack of rotor postion I can inadvertently produce space vector of the stator current in opposition to space vector of magnetic flux of the permanent magnets. Are my worries justified? \$\endgroup\$ – Steve Jan 17 at 14:46

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