Can a 3-phase permanent magnet synchronous motor be driven by power amplifier?

[David Lin]

I am trying to drive a permanent magnet synchronous motor(PMSM) with
pure sinusoidal drive voltage instead of SPWM. So I tried to use three
power amplifier OPA547 to amplify the 3-phase sin voltage input to
drive the motor. But the outputs of the OPA547 have obvious distortion
when the motor was at standstill or when it rotated. Then I tried to
drive the motor in 6-step stepping mode still using the OPA547, and
this time, the the outputs of the OPA547 have no distortion when the
motor was at standstill, but they distorted when the motor was
rotating. It seems the distortion was possiblly caused by the back
EMF. But why the power amplifier's output can be affected by the load?
Does anyone know how to drive a PMSM using linear power amplifier
instead of SPWM? If the OPA547 is not the right chip, which chip
should I use? Thanks a lot in advance.

 

[John Popelish]

I am trying to drive a permanent magnet synchronous motor(PMSM) with
pure sinusoidal drive voltage instead of SPWM. So I tried to use three
power amplifier OPA547 to amplify the 3-phase sin voltage input to
drive the motor. But the outputs of the OPA547 have obvious distortion
when the motor was at standstill or when it rotated. Then I tried to
drive the motor in 6-step stepping mode still using the OPA547, and
this time, the the outputs of the OPA547 have no distortion when the
motor was at standstill, but they distorted when the motor was
rotating. It seems the distortion was possiblly caused by the back
EMF. But why the power amplifier's output can be affected by the load?
Does anyone know how to drive a PMSM using linear power amplifier
instead of SPWM? If the OPA547 is not the right chip, which chip
should I use? Thanks a lot in advance.

Are you sure the current limit is set well above the peak current the
motor passes? Synchronous motors have poor power factor, so a lot of
inductive current unless the applied voltage is just barely enough to
maintain synchronism.

By the way, what supply voltage are you using? What maximum peak ot
peak voltage are you trying to apply to the motor?

 

[David Lin]

Are you sure the current limit is set well above the peak current the
motor passes? Synchronous motors have poor power factor, so a lot of
inductive current unless the applied voltage is just barely enough to
maintain synchronism.

By the way, what supply voltage are you using? What maximum peak ot
peak voltage are you trying to apply to the motor?

Hi, John, Thanks for your help. Yeah, I think the current should be
within the limit which is set to be 700mA. The peak2peak value of
terminal voltage of the motor is only 1.5V and the resistance of one
phase is about 4.5Ohm, which means the current should be below 500mA.
The OPA547 is powered by +15v and -15V.

 

[John Popelish]

Hi, John, Thanks for your help. Yeah, I think the current should be
within the limit which is set to be 700mA. The peak2peak value of
terminal voltage of the motor is only 1.5V and the resistance of one
phase is about 4.5Ohm, which means the current should be below 500mA.
The OPA547 is powered by +15v and -15V.

Okay then, I'm stumped. Have you checked the output with 4.5 ohm
resistors in place of the motor windings?

 

[R.Legg]

I am trying to drive a permanent magnet synchronous motor(PMSM) with
pure sinusoidal drive voltage instead of SPWM. So I tried to use three
power amplifier OPA547 to amplify the 3-phase sin voltage input to
drive the motor. But the outputs of the OPA547 have obvious distortion
when the motor was at standstill or when it rotated. Then I tried to
drive the motor in 6-step stepping mode still using the OPA547, and
this time, the the outputs of the OPA547 have no distortion when the
motor was at standstill, but they distorted when the motor was
rotating. It seems the distortion was possiblly caused by the back
EMF. But why the power amplifier's output can be affected by the load?
Does anyone know how to drive a PMSM using linear power amplifier
instead of SPWM? If the OPA547 is not the right chip, which chip
should I use? Thanks a lot in advance.

What sort of distortion?

The output will likely show some deviation as it changes over from
sourcing current to sinking current. This should occur at a
recognizable phase angle with the motor stalled.

It will also occur if the phases are 'slipping'with respect to the
drive source due to the motor's physical inability to match the drive
source frequency.

Why is distortion a concern?

RL