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Old 09-25-2015, 06:14 PM   #2083 (permalink)
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Originally Posted by danibjor View Post
If you look at the scematics on the patent, they use a rectifier between the mains and the motor - so you feed it with DC, not AC voltage. No sine wave = no rotations?

But I guess the controller have to know about what's happening, so it could go into "regen" mode?
two important points:
1) rectified AC is not smooth DC. It's actually quite "lumpy." Basically what any rectifier does is invert the negative part of the sin wave to be positive. A full wave rectifier with a 60Hz sin wave input will have a 120Hz set of all positive waves (half wave lumps). It's not smooth DC yet; that will require further filtration.
2) Standard Boost converters put a pulsed voltage into an inductor for their operation. It would be possible to use the motor controller to switch the IGBT's for this job. The inductor stores part of the energy, then releases it the next cycle. The need to store part of the energy drives the inductor size for the converter. Using a higher switching frequency allows a smaller inductor, to a point. MPPT boost converters will vary the duty cycle depending on the part of the rectified "DC" waveform present. This will help keep current and voltage in phase.

Anyway, as shown in the drawings, one phase leg of the 3 phase motor will have current flowing through it. This current won't be alternating, as in reversing sign. However it won't be DC constant. Further, even if it were constant DC, current flowing in the phase leg would cause the magnets in the rotor to align with the stator. Yes, it won't rotate around, but it could move up to about 45 degrees in a 4 pole pair BLDC motor.

This is the main problem I see with using a BLDC motor. I don't think it would be an issue for an induction motor, because you wouldn't induce current in the rotor. I don't know how wye vs delta connection would affect it's operation in an induction motor. Perhaps there's a clever way to put exactly opposite currents into a BLDC motor such that a net zero torque could be produced? The charger would have to know the rotor's position and somehow connect to all three phases to pull that one off.

- E*clipse
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