Does sensored position require output voltage feedback?

[christophertsch]

Is it necessary to read a the 3-phase output voltage feedbacks for KMS sensored position mode to work to control a permanent magnet motor?

Is it necessary to configure this lack of feedbacks or does the sensored position algorithm just not use the voltage inputs?

[christophertsch]

Thanks for the quick response Philip.

Just to be completely clear we are saying that when using sensored position (or speed for that matter) the output voltage analog inputs are not required for the KMS algorithms to work correctly.

[philip_drake · Accepted solution]

The field oriented control (FOC) used by KMS and by the NXP reference projects all use the 3 phase current measurements.  The current passes through a sense resistor and the differential voltage across the sense resistor is fed through an op-amp, amplified and provided as a +-1.65 Voltage input, centered on 1/2 VDDA.  This is a voltage input to the ADC that represents the current through the sense resistor. 

The other voltage measured is the DC bus voltage.  There is a simple resistor divider from Vbus, filtered and brought into another ADC channel.  This is a single ended voltage measurement with a VSSA reference. 

When you say the output voltage analog inputs are not required I'm thinking you may be thinking about the BEMF voltage measurement done for sensorless BLDC trapezoidal control.  The FOC method do not use the BEMF voltage.

Regards,

Philip 

[philip_drake]

The position in the sensored position KMS project is taken from the encoder inputs. 

The motor operation is still being controlled with FOC using the DC bus voltage along with the three phase current readings.

Are you trying to design your own board?  If so you can use the FRDM-MC-LVPMSM board as a good reference.

Regards,

Philip