Electronic – Relationship between offset in electrical angle and BLDC motor performance

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I am controlling a BLDC motor using Field Oriented Control (FOC). I use a 14-bit absolute encoder to read the rotor's position \$\theta_{m} \$, and use it to reconstruct the electrical angle \$\theta_{e}\$, which is given by:

\$\theta_{e}=\theta_{m}\cdot N_{p} + \theta_{offset}\$

This angle is used in Park's transformations to reconstruct current readings, and to produce, with inverse transform, PWM voltage references.

Given knowledge of the number of pole pairs \$N_{p}\$, and a perfectly homogeneous distribution of the pole pairs, how sensitive is motor's performance to the accuracy with which we experimentally define \$\theta_{offset}\$?

How accurately is it usually defined for high-accuracy torque control application field such as robotics?

Edit: with some more research, I found \$\theta_{offset}\$ accuracy is mostly sought for torque efficiency. What I am surprised not to find yet is people discussing its induced disturbances on the closed-loop current control systems. How does it affect, for instance: bandwidth, vibrations, audible noise, and energy consumption?

Best Answer

In my experience (with my own FOC design) \$ \theta_{offset}\$ errors primarily affect torque efficiency and bandwidth, and have a lesser or insignificant effect on vibration and audible noise. Small valued errors will result in 'lopsided' performance, where your motor spins faster in one direction than the other.

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