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Does the brushless servo motor need to measure the phase voltage? What is the pu

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Siwastaja:
The idea is simple to understand, you need to know in which position the rotor is, so that you can apply correctly aligned magnetic field (simplified: turn the right windings on!) that the magnetic field pulls/pushes the rotor forward.

Yes, the options for rotor position sensing are mechanical or optical encoders, or hall sensors that sense the permanent magnets of the motor. Sensorless is relevant in low-cost devices that do not need to run at low speeds at all. For example, drone motors are typically sensorless, but hoverboard motors have sensors because they need to run reliably at low speeds.

Minimum accuracy for acceptable drive is something like +/-30 electrical degrees, which is achieved by the classical configuration of three hall sensors installed in such way you get 6 distinctive steps per electrical rotation. But a servo which is accurately controlled and ran at low speeds, benefits from higher accuracy encoder than that.

If you want to just run the motor at optimum efficiency (as in traction devices), you want the generated magnetic field to be 90 degrees "forward" of the rotor position. OTOH, if you keep it at 0 degrees forward, you can hold the motor stalled, consuming current (of the resistive losses) in the process, resulting in 0% efficiency as no physical work is done. In a servo drive, efficiency and accuracy of control can be both have by gearing down the motor so that even if machine runs very slowly, the motor can run at some clearly non-zero speed, allowing feedback loops (FOC iq, id currents, and current setpoints based on measured speed) to run properly, maintaining high efficiency.

Benjam:

--- Quote from: Siwastaja on December 04, 2021, 06:22:23 pm ---The idea is simple to understand, you need to know in which position the rotor is, so that you can apply correctly aligned magnetic field (simplified: turn the right windings on!) that the magnetic field pulls/pushes the rotor forward.

Yes, the options for rotor position sensing are mechanical or optical encoders, or hall sensors that sense the permanent magnets of the motor. Sensorless is relevant in low-cost devices that do not need to run at low speeds at all. For example, drone motors are typically sensorless, but hoverboard motors have sensors because they need to run reliably at low speeds.

Minimum accuracy for acceptable drive is something like +/-30 electrical degrees, which is achieved by the classical configuration of three hall sensors installed in such way you get 6 distinctive steps per electrical rotation. But a servo which is accurately controlled and ran at low speeds, benefits from higher accuracy encoder than that.

If you want to just run the motor at optimum efficiency (as in traction devices), you want the generated magnetic field to be 90 degrees "forward" of the rotor position. OTOH, if you keep it at 0 degrees forward, you can hold the motor stalled, consuming current (of the resistive losses) in the process, resulting in 0% efficiency as no physical work is done. In a servo drive, efficiency and accuracy of control can be both have by gearing down the motor so that even if machine runs very slowly, the motor can run at some clearly non-zero speed, allowing feedback loops (FOC iq, id currents, and current setpoints based on measured speed) to run properly, maintaining high efficiency.

--- End quote ---


Wow...You are very professional. Thank you for your kind reply. ;D

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