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These resources are very helpful to understand BLDC motor control:
Benjamin Vedder’s VESC project: http://vedder.se/2015/01/vesc-open-source-esc/
Link to a great explanation of operating points and speed, current, torque, etc: https://things-in-motion.blogspot.com/2019/05/understanding-bldc-pmsm-electric-motors.html
Texas Instruments InstaSpin motor control algorithm: https://training.ti.com/introduction-instaspin-bldc-motor-control-solution
Motor and motor controller documentation.
Back-EMF and Kv
http://learningrc.com/motor-kv/
Our motor speed is limited by the back-emf of the motor, which is the voltage produced by the coils when the magnets are rotating around it. We are typically able to calculate this by using the Kv value of the motor (rpm / volt) and a known rpm. When this back-emf voltage equals the supply voltage, then we we can no longer produce any torque since there is no voltage difference to drive current through the motor phase coils.
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Kv (rpm/V) = max speed (rpm) / bus voltage (V)
Coil | Eco/PWM Graph | Kv (rpm/V of back-emf) |
|---|---|---|
HI | PWM | 5.6412 |
LO | PWM | 4.8702 |
HI | ECO | 6.0153 |
LO | ECO | 5.2061 |
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We will go with Kv = 6 for the worst-case phase current according to the estimations above, however I would love to measure the Kv rating of the motor once we get it hooked up to the test stand.
I made this excel sheet and tried to do more with it than I was able to, so some of the data is irrelevant and incorrect but you can have a look at it if you want.
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