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| Driving 3-phase motor from 2 amplifier phases |
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| Benta:
I look forward to seeing your sim, this sounds strange. Soldar, stop trolling. |
| Dave:
Mentally shift the whole phasor diagram so that point b sits in the origin. This is now ground. Vector ba is now sitting at 30°, vector bc is at 90°. They are 60° apart. So, you drive points a and c with voltage sines that are 60° apart and you have your balanced 3-phase signal. That's it. That's all there is to it. ::) |
| jmelson:
A permanent magnet motor cannot be started by just applying constant-frequency 3-phase power to it. You need to apply a very low frequency, low voltage drive, and then ramp up the frequency and voltage simultaneously, so the motor can stay in sync with the AC excitation. An induction motor can start with constant frequency excitation because the rotor magnetism can slip and stay in sync with the stator field. Jon |
| Kalin:
Is this the same concept as a synchronous 3 phase motor? If so does it actually need a ramp in frequency or could it be done in discrete steps say 10-20-30hz. Sent from my SM-G965W using Tapatalk |
| duak:
Kalin, I developed the analog and power sections of an ultraprecision BLDC motor system. Until the DSP portion with an encoder was completed, for testing I drove the motor with arbitrary frequencies. My experience is that a smooth ramp is required and the rate depends on the motor and its load. The motors I worked with might tolerate a 1 or 2 Hz jump, but not much more. When DC currents were applied to the motor, you could turn the motor shaft back and forth and it felt just like a spring. If you let it go, it would oscillate like a balance wheel in a clock. So while the rotor in the motor tends to follow the magnetic field generated by the windings, if they get out of sync, there's no net torque on the rotor and it slows down to a stop. Cheers, |
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