Motor Quadrature encoder and UVW outputs

[JoeyG]

I have a motor with encoder that has a Quadrature encoder output AND  a UVW output.

My motor controller mcu has  Quadrature encoder  hardware decoder  a but I wonder what the advantages of using the UVW outputs are.

The motor is a  3 phase  PMSM (or BLAC) / BLDC .

What would be the advantage of UVW?

My internet search only review limited results

[Doctorandus_P]

UVW is probably intended for direct phase control. In such a case they are connected directly to power switches, and this turns the motor into a "brushed" DC motor, but without the brushes (and their wear and reliablity issues).

With UVW you also have a direct indication of the magnetic pole position of the motor. With quadrature, you need some extra way to calibrate the "zero" position of the motor axis.

[jwet]

This has changed some in the last 20 or so years as sensors and IC's have entered the scene.

UVW are commutation control outputs and are traditionally aligned with the structures in the motor- resolution is generally the small number of poles in the motor, angular accuracy is not great since traditionally separately mounted hall devices are used but read on. Quadrature outputs have traditionally been produced by an optical encoder with a slotted wheel and have much high resolution up into thousands- their phase is not aligned directly with the motor.  In a lot of modern BLDC motors, both of these outputs are produced by a rotary angle sensor from a single special magnet.  The input for both is the same and the outputs are synthesized.  In general, UVW are useful for speed control and commutation and incremental is used for precision angular displacement (stepper like).

The rotary angle sensors used have good app notes.  Sensima (acquired by MPS), Allegro and Melexis make most of the IC's.  You'll have to work your way through which is better in your case.  The synthesized outputs have different kind of errors from the old outputs and require some rethinking.

Good luck.

[mtwieg]

Not uncommon to see both hall sensor and quad encoder in a servomotor application. The hall sensors are used by the lowest-level motor controller, which implements speed control. The quadrature encoder can be used by a master controller implementing position/servo control, with the speed controller as its slave.

The quadrature encoder could also be used a redundant sensor for functional safety.